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The One-Minute Workout: Science Shows a Way to Get Fit That’s Smarter, Faster, Shorter

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Finally, the solution to the #1 reason we don’t exercise: time. Everyone has one minute.
A decade ago, Martin Gibala was a young researcher in the field of exercise physiology—with little time to exercise. That critical point in his career launched a passion for high-intensity interval training (HIIT), allowing him to stay in shape with just a few minutes of hard effort. It also prompted Gibala to conduct experiments that helped launch the exploding science of ultralow-volume exercise. Now that he’s the worldwide guru of the science of time-efficient workouts, Gibala’s first book answers the ultimate question: How low can you go?
Gibala’s fascinating quest for the answer makes exercise experts of us all. His work demonstrates that very short, intense bursts of exercise may be the most potent form of workout available. Gibala busts myths (“it’s only for really fit people”), explains astonishing science (“intensity trumps duration”), lays out time-saving life hacks (“exercise snacking”), and describes the fascinating health-promoting value of HIIT (for preventing and reversing disease). Gibala’s latest study found that sedentary people derived the fitness benefits of 150 minutes of traditional endurance training with an interval protocol that involved 80 percent less time and just three minutes of hard exercise per week.
Including the eight best basic interval workouts as well as four microworkouts customized for individual needs and preferences (you may not quite want to go all out every time), The One-Minute Workout solves the number-one reason we don’t exercise: lack of time. Because everyone has one minute.
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			The Tabata Classic

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			In the 1990s, the head coach of the Japanese speed skating team, Irisawa Koichi, had his athletes employ a brief but intense workout that featured short bursts of high-intensity exercise followed by even shorter rest periods. A coach on the team, Izumi Tabata, was the first to analyze the workout’s effect, lending his name to a protocol that helped kick off the interval-training movement. Many personal trainers still love the format today. Note that Tabata’s study used exercise bikes, although virtually any activity that significantly elevates the heart rate can be used.

			Peak Intensity • 9

			Duration • 9 minutes

			The Evidence • Tabata’s 1996 paper compared what’s now known as the Tabata protocol with moderate-intensity endurance training. The endurance group performed 5 days of endurance testing per week for 6 weeks, while the sprint group conducted the interval protocol four times a week, plus one 30-minute steady-state workout per week at a moderate pace. After 6 weeks, the aerobic capacity of the endurance group hadn’t improved at all. But the sprint group, which had conducted hard exercise for a little less than 11 minutes per week, had improved its aerobic capacity by 14.6 percent—making Tabata’s study one of the first to show how potent sprints could be as a tool to improve aerobic capacity.

			Who Should Do It? • Tabata originally conducted the study with athletic college-age phys ed students, most of whom were on varsity teams for such sports as soccer, basketball, and swimming. With recovery periods that are shorter than the sprint periods, and near-maximal effort, Tabatas are tough. Most people who perform Tabata-style workouts consider themselves hard-core athletes.


					Warm up at an easy pace for about 3 minutes.

					Sprint for 20 seconds at intensity 9—not quite all-out.

					Rest for 10 seconds.

					Repeat the 20-seconds-on, 10-seconds-off cycle for a total of 8 sprints.

					Cool dow; n with some light activity for 2 minutes, for a total workout duration of 9 minutes.



			It’s easy to include resistance training within the Tabata protocol. In 2012 my colleagues at Queen’s University and the University of British Columbia’s Okanagan campus created one of the most elegant ways to meld time-efficient intervals with resistance training. They based it on the Tabata format but replaced the sprints with resistance-training exercises—with remarkable results.

			Recreationally active female university students conducted the protocol, although the benefits would apply to healthy men and women of all ages. With 4 minutes a day of intense exercise, the subjects improved aerobic fitness as much as a comparison group did conducting vigorous-intensity endurance exercise for 30 minutes per day. In addition, the test subjects increased the number of leg extensions they could do by 40 percent, the number of push-ups by 135 percent, and the number of sit-ups by 64 percent, among other measures. The takeaway? A Tabata bodyweight protocol is a potent way to simultaneously boost aerobic capacity and muscle strength. Here’s how to do it:

					Each training day, begin with a 3-minute warm-up of your chosen exercise by performing light versions at a slow pace.

					On Day 1, complete as many burpees as you can in 20 seconds. To complete a burpee, begin in a standing position. Squat down, place your hands on the floor with your palms down, and kick both legs out behind you so that you end in a plank position. Return to a squat position, and leap up into the air as high as you can while raising both arms above your head. To increase the difficulty, perform a push-up from the plank position.

					Rest for 10 seconds.

					Perform the exercise for 20 seconds, trying to complete as many reps as possible. Cycle through the 20-seconds-on, 10-seconds-off format until you’ve completed 8 bursts of the exercise.

					Cool down for 2 minutes, for a total workout duration of 9 minutes.

					On subsequent training days, perform the 20-second-on, 10-second-off cycle for 8 repetitions with the following exercises, concentrating on just one exercise per day: mountain climbers, jumping jacks, or squat-thrusts.

					To perform a mountain climber, start in the plank position. Staying in the plank, bring one leg forward so the knee approaches the chest. Return to the regular plank. Then bring the other knee forward so the knee approaches the chest. Repeat.

					To perform a jumping jack, begin standing up straight with your hands at your sides. Jump and land with your legs set slightly wider than shoulder-width apart and your arms raised above your head so that the fingertips nearly touch. Do a second jump to return to the standing position, with your arms hanging by your sides. Repeat.

					To perform a squat-and-thrust, begin standing straight with your hands at your sides. Squat down until your hands are flat on the ground. Kick your legs out behind you so that you end in a plank position. Bring in both legs at the same time to return to a squat, and stand up with your arms at your side. Repeat. Note that the study subjects used 5-pound dumbbells, but in the interests of simplicity we’ve dispensed with the equipment. To increase the difficulty of the squat-and-thrust, incorporate a push-up when planking.

					Eager for more variety? Rather than doing one exercise per day, consider changing things up so that you’re alternating circuit-style between all four exercises within the protocol on the same day.



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			The Workouts



			Title Page



			Fit in Just Minutes a Week?


			How Intensity Works


			How It All Got Started


			Beyond Simple Fitness


			High-Intensity Engagement


			Fun and Fast: Eight Basic Workouts


			How Low Can You Go? Four Potent Microworkouts


			High-Intensity Nutrition


			The Perfect Exercise for You



			About the Author




			The Beginner

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			HIIT sounds daunting—like it’s available only to those who are ultrafit. But even if your only physical activity is walking, you, too, can benefit from an interval approach.

			Peak Intensity • 3

			Duration • 30 minutes

			The Evidence • Walking is the best medicine, according to many doctors. It’s easy, convenient, and cheap. The problem is that some people’s pace may not be fast enough to increase their physical fitness. So a group out of Japan’s Shinshu University pioneered interval walking for older people who don’t do much physical activity, kick-starting a whole series of studies on the topic. In general, these protocols involve speeding up the pace for around three minutes, easing off for about the same amount of time, and then pushing up the pace again. Compared with walking at a steady pace, the interval-based routine has been shown to result in much larger improvements in cardiorespiratory fitness and much larger decreases in blood pressure for those who are out of shape. More recently, a 2013 study out of the University of Copenhagen showed that an interval-walking approach cut fat mass and body mass and improved the ability of people with type 2 diabetes to control their blood sugar, while continuous walking did not. The interval-walking protocol we’ve used here is drawn from a 2010 joint effort out of the Mayo Clinic and Shinshu University. That study showed that three months of interval walking repeated four times a week increased cardiorespiratory fitness by more than 25 percent and spurred a 6 percent reduction in systolic blood pressure—the important first, higher number of any blood pressure reading. The Mayo Clinic–Shinshu University study subjects averaged 34-minute-long bouts of interval walking. I’ve capped the workout at 30 minutes here, but feel free to go longer for incrementally additional benefits.

			Who Should Do It? • The Mayo-Shinshu study featured out-of-shape men and women in their mid-fifties. Previous studies have used this format on people in their late seventies who were so sedentary that three minutes of fast walking was the longest they could manage in a single effort. So this program could be well suited to seniors or really anyone just beginning an exercise regimen.


					Warm up by walking at an intensity of 1 for 3 minutes.

					Increase your effort to intensity 3, so you are breathing deeply but could still maintain a conversation. Hold that pace for 3 minutes.

					Ease back to intensity 2 for 3 minutes.

					Repeat steps 1 to 3 for a total duration of 30 minutes.

					Don’t feel bad if you can’t manage 30 minutes of interval walking right away—start with as many repeats as you can manage and then work your way up.



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			Fun and Fast: Eight Basic Workouts

			I design my own workouts all the time. I go down into my basement, hop on the exercise bike, turn on some sports on the television, and get to it. Sometimes I’ll perform various bodyweight exercises between sprints. Push-ups, pull-ups, burpees—you name it. Each of these amounts to strength-building resistance training that will help me stave off the effects of aging. Creating workouts is one of the fun things about exercise. It keeps things fresh.

			This chapter is all about providing people with the tools to create their own high-intensity interval training workouts. The difference between these workouts and those in most other exercise books is that the benefits of these programs have been scientifically proven. Below, I include eight workouts that have been featured in peer-reviewed academic studies—protocols used on everyone from cardiac rehabilitation patients to high-caliber athletes. I describe the workouts’ scientifically assessed benefits and finish with some tips to help you design your own. But first, a few words about how we quantify “effort.”

			Fast and Furious: Assessing Intensity

			Envision a typical spin class. A trainer straddles a bike that faces a dozen clients on exercise bikes. Shouting loud enough to be heard over a pounding techno beat, she barks into her headset: “Give me 90 percent in three . . . two . . . one . . . And go!” All around the room, veterans and first-timers alike mash their pedals. But chances are they’re all working at different rates—because they have different perceptions of what a 90 percent effort feels like.

			Which brings us to one of the trickiest elements of high-intensity interval training: How do you convey to someone the effort required for a given sprint? Many different ways exist to measure exercise intensity. But most of them have been designed to work with long-duration continuous aerobic workouts—and, when applied to sprints, each of them comes with its own idiosyncratic problems.

			Vo2max and Power

			Traditionally, the most precise way to determine workout intensity involves measuring how much oxygen a person uses during exercise. We express that measurement relative to the person’s maximal oxygen uptake, or VO2max. So we might say a person is cycling at 75 percent of their VO2max. However, several problems exist when using VO2max to describe the effort expended in intervals. In a sprint, it’s possible to run many times faster than the pace needed to elicit your VO2max. And measuring VO2max is unwieldy, requiring a mask over the mouth and nose, and breathing tubes leading to a device that measures the difference in the oxygen content of the air the subject inhales and exhales. It’s just not practical outside a lab.

			Another scientific measure of exertion is power, which is most commonly measured in watts. The same unit is used to describe the brightness of a lightbulb or the energy efficiency of your fridge. A watt is a measure of the rate that work is done. On a bike, healthy but untrained people might reach their VO2max at a power output of 300 watts—but in a sprint, that same person can generate 900 watts for a few seconds, while elite track cyclists can achieve 2,000 watts or more. That’s a work rate that could light twenty 100-watt bulbs—enough to illuminate an entire large house. The trouble with that measure? We want each of these workouts to be adaptable to many different forms of exercise. While computers can easily measure watts on exercise bikes, it’s hard to determine power output with other activities such as swimming or running.

			The Trouble with Heart Rate

			Another common way to describe exercise intensity is relative to a person’s maximum heart rate. (A convenient way to estimate this value is 220 minus your age, although a lot of variation exists between individuals.) “Go for a run at 65 percent of your maximum heart rate,” one trainer might say—a rate of exertion that would see a typical forty-year-old aim for an average heart rate of 117 beats per minute. That’s a lot easier to measure outside the lab because heart-rate monitors are getting more portable and accurate all the time.

			The trouble is, heart rate is also a problematic measure to describe the intensity of maximal and near-maximal sprints. Because heart rate lags effort, especially at the start of intense exercise. “Go as hard as you would to save your child from an oncoming car,” I tell people when I want them to give me an all-out sprint. But after a thirty-second all-out sprint, your heart rate might get up to only about 70 percent of its maximum. That’s because when you exercise very vigorously, it takes the cardiovascular system a bit to catch up. The only time you reach your maximal heart rate is through hard aerobic exercise sustained over a few minutes, or over the course of repeated sprints with very short recovery periods. So while the percentage of maximum heart rate works well as an indicator of exertion during steady-state aerobic exercise, and it can even be adopted for less-intense sprints, it’s a lot more problematic for describing the exertion required to sprint at an all-out pace.

			So What’s the Answer?

			The solution begins with something physiologists call rating of perceived exertion, or RPE. The psychologist Gunnar A.V. Borg of the University of Stockholm introduced the concept in 1970. Borg tied his rating of perceived exertion to heart rate. The original scale went from 6 to 20—a range that roughly matched the heart rate of an average young person divided by 10; it began at 6 because an average young person’s heart rate is around 60, and it went up to 20 because that same young person’s heart rate tops out at about 200 beats per minute. Walking, or “light” exercise, would correspond to an RPE of 10 or 11.

			A scale from 6 to 20 is a bit unwieldy, so Borg subsequently came up with a simpler RPE range from 1 to 10, with 1 being described as “nothing at all” and 10 as “very, very strong (near max).”

			The intensity scale of the workouts described in this book is modeled on Borg’s revised RPE scale. Note that, as with Borg’s scale, it’s possible to go higher than 10 here as well. Looking at the following chart, you’ll see that the “10+” rating indicates an all-out sprint—equal to my old descriptor of “as fast as you would go if you were saving your child from an oncoming car.” To provide a rough guide, the figures below match exertion levels with the proper score on Borg’s revised scale.

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			Visit for a larger version of this chart.


			What’s with the Ascending Exertion Ratings for Some Workouts?

			Because I perform most of my workouts on my home exercise bike—a Life Fitness 95Ci, to be specific—I tend to base my own sprint workouts on absolute workloads, which tie the outputs to a specific workload that I have to maintain. My bike allows me to plug in a certain power setting—say, 250 watts. And then I’ll do five intervals of five minutes apiece with a minute of recovery. My heart rate climbs throughout the five sprints—and I know that last interval is going to be a beast. I like it because the challenge increases over the course of the workout. When I finish, I know I’ve given my all. I’m really spent—and I feel great.

			Which brings us to one facet of the workouts you may already have noticed if you skipped ahead. Some of the exertion ratings increase through the course of the workouts. That’s because I’m basing the workouts on protocols featured in the actual scientific studies that established the remarkable potency of high-intensity interval training. Some workouts are based on sprints with near-maximum or maximum efforts. In those cases, the person’s power output or actual speed declines with each successive sprint—because the all-out effort of the previous sprint is tiring and makes less energy available for the next sprint.

			However, some of these workouts are based on studies that required the subjects to generate the same power output with each sprint, regardless of whether it was the first or the last rep. These workouts tend to feature sprints that are intense, but something less than all-out. So, for example, in the study that established the potency of the Ten by One protocol, we asked the subjects to pedal at the same power output all the way through the workout. And to do that, they had to work a little harder each time. (The analogy holds for other types of interval training. For example, if you’re a runner, envision being asked to run up the same hill at the same speed ten times in a row—of course, you would have to exert more effort to achieve the same speed through each successive hill run.)

			Hence, the increasing exertion rating for the workouts that are intense but not all-out. Because we’re citing studies that scientists conducted with absolute workloads, the exertion level would have increased throughout them. And to be sure you’re getting the same benefits as the study subjects, you should increase your exertion throughout the workout as well.

			A Few Quick Words About Calories

			Many exercise books note the calories burned in a given workout. So do exercise bikes. The one in my basement even takes into account variables like the workload setting and duration, as well as my weight and age. But the “calories burned” measure is really just an estimate—an average for people like me. It’s not an exact measure because no exercise bike can know every one of the variables that influence the number of calories burned. So many factors influence that statistic, including your own genetic makeup.

			Also, we intend these exercises to be templates applicable to just about any aerobic exercise, from cycling and running to repeating burpees and stair climbing. The number of calories burned also changes depending on the type of exercise you’re doing. And finally, there’s the notion of afterburn—a word that trainers often use to describe the increased number of calories your body expends while recovering from the exercise. The more technical term for the phenomenon is “excess post-exercise oxygen consumption,” or “EPOC,” and it is influenced by the intensity of the exercise you’ve just done. The more intense the exercise, the higher the number of calories consumed in the afterburn. (We’ll discuss EPOC and intense exercise more in chapter eight.)

			The point is, we can’t provide you with the exact number of calories burned during these workouts because it depends on the actual workload as well as your own physiology. Suffice it to say that when you factor in the afterburn, all the workouts described in this chapter consume more calories than an equivalent period of traditional steady-state exercise. For some of the workouts, we have verified this directly in the lab. For example, the Ten by One elicits an increase in energy expenditure (that is, calories burned over twenty-four hours) that is similar to a bout of moderate-intensity continuous exercise lasting about twice as long.

			Modifying Your Interval Workout

			The following workouts are only suggestions. Feel free to change them any way you see fit. That’s the beauty of interval workouts. They can be variable to a nearly infinite degree. One thing I’d suggest considering is figuring out a way to get comfortable incorporating some resistance training into your workouts. That’s because resistance training becomes increasingly important the older you get. It’s the sort of exercise that builds strength; it encompasses weightlifting, bodyweight movements like push-ups and pull-ups, kettlebell training, and workouts using the Universal machines you see in fitness centers.

			It’s well established that combining aerobic and resistance training reduces body fat better than aerobic exercise alone. The resistance training also combats the muscle-wasting effects of aging. And it makes you look better.

			Happily, many interval-training protocols are well suited to incorporate resistance training. Several different approaches exist—and each one tends to be hyperefficient, because it works a lot of different physiological systems in a short amount of time. One involves performing bodyweight exercises during the “rest” portions. So in the four and a half minutes of rest specified between thirty-second sprints in the Wingate Classic, for example, you might perform squats, burpees, push-ups, or pull-ups. The trouble with this approach is that the resistance training tires you out, so you have less energy available to devote to performing your sprints.

			The way that I prefer, which also happens to be the way that many personal trainers do things, involves bodyweight exercises, or resistance-training movements in which the body is the “weight” lifted. Whether we’re talking push-ups, pull-ups, burpees, squats, or the dozens of other variations, bodyweight exercises work many different muscle groups, which means they also elevate the heart rate. Performing them quickly exercises the aerobic system—which in turn means that bodyweight exercise can be performed as interval-training sprints.

			So to incorporate resistance training into a sprint workout, simply swap out the run, swim, or cycling activity with any bodyweight exercise that elevates the heart rate to a similar extent. The trick is to avoid workouts with long-duration sprints, because few people can perform bodyweight exercises for any significant length of time. I wouldn’t try to adapt the Norwegian workout to a bodyweight approach, for example, because the four-minute-long intervals will be too tough if you do push-ups for your sprint intervals.

			Among the protocols in chapters six and seven, the Fat Burner and the Tabata Classic both work well with bodyweight sprints, as does the Ten by One. But feel free to experiment with the protocols and customize them to your particular needs. I have a favorite bodyweight-sprint workout that involves ten minutes’ worth of thirty-second-on, thirty-second-off intervals. The first thirty-second work interval is a warm-up exercise of jumping jacks. The second “on” interval is push-ups. The third is pull-ups from a bar, and the fourth is squats. Then repeat the cycles of push-ups, pull-ups, and squats until you’ve conducted three sets of each, for a total workout duration of ten minutes. It’s fun, and super time-efficient because I’m getting in my daily resistance and aerobic training in less time than it takes to walk the dog.

			Team sports are another way to incorporate interval workouts into your fitness routine. My family is crazy about team sports. I play hockey once a week. My wife plays both hockey and soccer, usually on multiple teams a season, and both my sons play competitive hockey. Such experiences have provided me with many opportunities to observe how those playing team sports can incorporate interval-based physical activity without actually performing a specific interval workout.

			Think about it: In hockey, on a team with three full lines, a typical shift is thirty to forty-five seconds long. The shift amounts to a sprint—a nearly all-out burst of activity that leaves me huffing for breath, and my heart pounding, fifteen to twenty times a game. Hockey is a great interval workout.

			So is soccer, with its breakaways and runs into space; players can jog more than six miles in a professional game. Full-court basketball qualifies as an interval workout, too. As do Ultimate Frisbee and touch football. In fact, many team sports amount to the best kind of sprint sessions. Conducted with friends, at near all-out intensities, they likely provide their participants with plenty of benefits.

			But how much? A fellow academic from my hockey group, McMaster’s Peter Kitchen, coauthored a 2016 study that found that male recreational hockey players ages thirty-five and over tend to have lower rates of diabetes, high blood pressure, and heart disease than do other physically active males.

			Similarly, a 2010 paper revealed that recreational soccer players took part in intense intervals, with their heart rates averaging higher than 90 percent of their maximum for 20 percent of the game, leading to increases in muscle mass and cardiorespiratory fitness that were greater than those in a comparative group of endurance runners.

			The point? If you’re looking for a fun, social alternative to interval workouts that nevertheless provides many of the same benefits, consider playing team sports.

			How to Approach the Workouts

			All the workouts described in this chapter are based on formats used in actual scientific studies. Some of these studies featured warm-ups and cool-downs that ranged from five to ten minutes long, whereas other studies did not explicitly describe such details. Most people will do fine with a three-minute warm-up and a two-minute cool-down, so in the interests of time-efficiency and consistency, that’s generally what is specified here. As you will see from the descriptions, certain workouts are more suited for certain types of people—whether beginners or those who have progressed further in their training. If you opt to set yourself on a path toward vigorous exercise, here’s how I’d approach things:

			Step 1: First, always check with a physician before starting or changing an exercise routine. Once you’ve received the all clear from your doctor . . .

			Step 2: If you’re out of shape, don’t try to be a hero. Mitigate the low risk that exists by starting with easy workouts and then working your way up to tougher ones. Don’t begin with all-out sprints. Instead, try an interval-walking program and move gradually to more intense workouts like the Ten by One and the 10-20-30 (both of which you can find in this chapter). We call these intense but submaximal protocols, because while the formats ask the participants to work out hard, the protocols don’t request all-out intensities.

			Step 3: Only when you’re comfortable with variations of submaximal interval protocols should you consider moving up to the expert workouts—the bodyweight circuit-training formats like the Tabata Bodyweight or Go-To workouts in chapter seven. Same goes for the really potent, ultratime-efficient all-out workouts such as the One-Minute Workout and the Wingate Classic. I’ll say it again: These are not for beginners—work up to them, and once you’re ready, feel proud that you’re in-shape enough to enjoy the benefits of the most potent, time-efficient exercises available.


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			The Workouts


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			Fit in Just Minutes a Week?

			Feel like you don’t have time to exercise? Looking for a way to get in shape—fast? Of course you are. Regular physical activity makes you look and feel better. You’ll also fight the aging process, go through your days in happier spirits, and reduce your chance of developing ailments like cardiovascular disease, diabetes, and even cancer.

			I think exercise is one of the best things around. Most of us are under the impression, however, that exercise has to be time-intensive. We have this notion that it takes at least an hour to get in a good workout—more if you factor in the time required to get to and from the gym.

			My studies show that idea is nonsense. The past decade has seen an explosion of research into the science of high-intensity interval training, better known by its acronym, HIIT, pronounced “hit.” We’re learning that HIIT can provide serious benefits that increase a workout’s time-efficiency. Sprint interval training, or SIT, which is the most extreme version of the technique and is characterized by a few brief bursts of all-out exercise, is especially potent. We’re not just talking running here. HIIT techniques can be applied to virtually any mode of traditional cardio-type exercises, such as cycling, swimming, or rowing. Thanks to the new science of ultralow-dose exercise, those who read this book will learn strategies to get fit in the time required to grab a coffee, update a Facebook status, or check a Twitter feed.

			Think for a moment about the traditional concept of what it takes to get fit. Most of us will envision an activity that requires hours and hours of hard work. Lots of miles pedaling in the bike saddle. Entire afternoons navigating running trails. Lap after lap at the local pool. Consequently, many people are too intimidated to even try to get fit. Many of us feel like there simply isn’t enough time to fit in a workout.

			But you know what? That’s wrong. That’s what my years of study have taught me. I’ve discovered that fitness is possible without spending countless hours in the gym. I don’t want to say that all the people who do that are wasting their time. But the fact is, a method exists that enables you to reap the benefits of hours of exercise in just minutes per day. Strategies can be incorporated to transform you from out of shape to fit in the least amount of time possible. Among my biggest discoveries is a workout that provides the benefits of nearly an hour of steady aerobic exercise with just a single minute of hard exercising.

			Pretty remarkable, right?

			This book is for the people who believe they don’t have time to exercise. In these pages, I describe techniques pulled from the latest scientific studies—how they work and how you can use them. I also provide tips on how to best manage your weight. And provide some easy methods to design muscle-building workouts that can be conducted anywhere from hotel rooms to your local park, with little or no need for special equipment.

			I know, I know—many personal trainers and workout celebrities promise such benefits. But they don’t have the deep scientific knowledge that comes from being a leading researcher in the field. The groundbreaking studies that have come out of my lab have been covered by the New York Times, Time magazine, and NBC Nightly News, to name just a few media outlets. In 2015, a review article that I wrote on the topic of time-efficient exercise was the most accessed paper in the Journal of Physiology, the world’s most cited physiology journal. In fact, the top two titles on the Journal’s annual ranking of most-accessed papers were from my laboratory, and we had three in the top fifteen. That’s quite a feat, considering all the amazing human physiology research that is conducted worldwide.

			I am also fortunate to work with a lot of great people. As the chair of the Department of Kinesiology at McMaster University in Hamilton, Canada, I interact on a daily basis with people whose assembly of brainpower ranks among the best on the planet. “McMaster is one of the centers of the universe when it comes to exercise,” observes Carl Foster, a physiologist at the University of Wisconsin–La Crosse and a past president of the American College of Sports Medicine. In fact, McMaster is a world-leading center of excellence in the study of how physical activity changes human physiology and health.

			With this book, I’ve drawn on the expertise of past and present McMaster minds and some of the smartest exercise physiologists in the world to create the most definitive guide to time-efficient exercise. I hope you’ll also find it’s an entertaining read. Once you’ve finished it, you’ll know enough to design your own time-efficient workouts. And you’ll have grasped the techniques required to go from out of shape to a buff portrait of health in the least amount of time.

			Already fit? If you’re not using the techniques described here, chances are you’re getting beat by someone who is. This book will provide you with techniques that can help you break through a training plateau and drop seconds or even minutes from your personal-best times. It’ll also allow you more time to do other stuff, like work or hang out with loved ones, because you’re not spending hours in the saddle, on the trails, or in the pool. And during those weeks or months when work or other duties make it difficult to exercise, this book will provide you with a series of techniques designed to maintain your fitness level in the minimum amount of time.

			So let’s get to discussing the most time-efficient workouts possible, for everyone from couch potatoes looking to get in shape to athletes wanting to boost their race performance. No longer do you have to fit your day around your workout. Now you can fit working out around your day.

			Introducing a More Time-Efficient Way to Work Out

			So what is interval training? Basically, it’s bursts of intense exercise separated by periods of recovery, which can involve complete rest or lower-intensity exercise. Understanding the concept is easier if you contrast it with regular endurance training. That’s the sort of thing most people envision when they think about heading out for a run. Or head out for a swim. Or a ride. The point is that traditional exercise training involves traveling a certain distance at a relatively constant pace. The resultant graph of effort versus time looks roughly like this:

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			That line of constant effort might stretch out to forty-five minutes, an hour, ninety minutes, or even more. When you can afford the time, it’s wonderful to get out and just run or ride with your mind at ease. That sort of training has a lot of therapeutic benefits. It reduces stress and can provide the opportunity to enjoy the outdoors. But my research has shown that it is anything but the most efficient way to train.

			If time is our most valuable resource, and if we’re attempting to get the most benefit from exercise in the least amount of time, then, as my research has shown, we’re better off employing interval-training techniques. The graph of an interval-training workout looks more like this:

				[image: ]

			The idea is to vary the intensity of your workout. Go hard, relax, go hard, relax. The harder you go, the shorter the duration and the fewer intervals you need to achieve the same benefits of a much longer endurance-training workout.

			People have been trying for centuries to get the benefits of exercise in creative ways that require less time. Think about hucksters wandering the Wild West promoting health elixirs or comic-book classified ads promising strongman muscles in mere weeks. More recently, the prestigious academic journal Cell published a study about a compound, known by the acronym AICAR, that helped sedentary mice run for 44 percent farther than untreated mice. The study raised a flurry of excitement about the possibility of developing an exercise pill, yet no one’s been able to replicate the results in humans.

			Interval training is the closest thing we have to an exercise pill. And over the past ten years there’s been an explosion of research into the technique. This research has been conducted in my own lab as well as those of my colleagues all over the globe. And researchers like myself have concluded that high-intensity interval training may be the most efficient workout that the science of physiology has ever produced. Neatly summing up its benefits, A. J. Jacobs wrote in Esquire, “HIIT could be the biggest time-saver since microwaves.”

			HIIT is so popular that it has ranked at or near the top of the annual list of worldwide fitness trends compiled by the American College of Sports Medicine, the largest sports medicine and exercise science organization in the world. Personal trainers everywhere from New York to Hong Kong are staging fitness classes based on principles I helped establish at McMaster, just as Hollywood stars and Victoria’s Secret models are using HIIT principles to get ripped for movie roles and fashion-week runway appearances. But here’s the thing: We’ve still got this idea in our heads that interval training is reserved for incredibly fit people working out in gyms in incredibly tight clothing. And doing workouts that last about an hour.

			Again, that’s nonsense. Workouts don’t have to last an hour. They can last ten minutes or even less—and get you remarkable fitness benefits in that time. Even if you’re overweight. Even if you’re out of shape. There is a “flavor” of interval training appropriate for you. This exciting new science of interval exercise can be adopted to help everyone get fit—especially the people who long ago wrote off exercise because they felt like they didn’t have the time.

			Want to get fit fast? Or just get up a flight of stairs without losing your breath? Interval training can help. Want to cut your Ironman time? Burn fat faster? Or simply increase how far you can pedal on your Sunday ride? Interval training can help with that, too.

			Most important, it can help in a lot less time than you ever thought possible. Interval training is perfect especially for the most time-pressed among us—everyone from city-hopping frequent-flyer executives to stay-at-home parents.

			Public health guidelines generally call for at least two and a half hours per week of moderate-intensity exercise to gain health benefits. Devoted fitness enthusiasts often schedule at least an hour per workout. Interval training is a way to get the benefits of an hour-long run or bike ride in a fraction of the time. In the most extreme form, known as sprint interval training, it’s possible to get those same benefits with just three minutes of hard exercise a week. In fact, my lab conducted the study that showed this—and the resultant news story rocketed to the top of the New York Times’ most-popular-articles list.

			I’m excited about this book for the same reason I’m excited about interval training itself—for their potential to make the benefits of exercise available to the greatest possible number of people. To that end I’ve tried to make this book a compelling instruction manual that’s written in plain language and understandable for those without a degree in physiology.

			I tell readers what interval training is, why and how it works, and who it works for. Then I provide a series of workouts and microworkouts that have been tested in laboratories around the world, followed by a discussion of the workouts’ benefits, which have been established through rigorous scientific study.

			The technique can be applied to pretty much any sort of exercise—and the most time-efficient versions include elements that boost both cardiovascular fitness and strength. Cycling, swimming, or bodyweight-style movements like burpees, push-ups, and pull-ups—they all accommodate interval-training techniques.

			Now, I’m excited to translate the latest science into training techniques that virtually anyone can use.

			How I Got HIIT

			These days, when I conduct interviews on television shows or in newspapers, the journalists call me things like the “guru” of interval training. This makes me a bit uncomfortable, especially given the training method’s incredible history (which we’ll consider in chapter three). It’s true that I’ve devoted most of my career to researching the topic. I’ve published dozens of academic studies in peer-reviewed journals over the past decade involving every aspect of interval training—how to do it, who can benefit, and how its potency compares with that of more traditional exercise approaches.

			Looking back to the beginning of my research, I can see why I started pursuing it when I did. In 2004 I had just begun my all-important second three-year contract as an assistant professor at McMaster University. Tenure is a tough thing to secure in academia, and I had less than thirty-six months to prove myself as an asset to the university—or be jettisoned from the faculty. It was my career’s ultimate make-or-break period.

			On top of the pressure to produce quality research, I was teaching three courses, including one to more than two hundred undergraduates. My wife, Lisa, had just gone back to work as a high school physical education teacher. We had two young boys, ages one and three. Juggling my child-rearing responsibilities with teaching and research meant that, for the first time in my life, I felt like I didn’t have time to exercise.

			I can remember coming home from my office hours and walking through my front door excited at the possibility of trying to squeeze in a workout. But then something would come up. The boys would need to be fed. Or we’d be out of milk. Somebody might have a fever. I’d put off exercising to cater to more pressing needs. It would be days or even a week before another chance to exercise would emerge.

			Interval training at that point was largely confined to the domain of highly trained individuals focusing on athletic performance. Few regular people ever performed interval-based workouts. Explaining why the average person didn’t appreciate the value of intervals requires learning a bit about the way the body works.

			Fitness means different things to different people. To exercise scientists, it means cardiorespiratory fitness, a parameter that can be measured in the laboratory by way of a test called maximal oxygen uptake or “VO2max” (the “V” stands for “volume”). It is also called aerobic fitness, and it refers to the capacity of your body to transport and utilize oxygen. Scientists have found that it’s one of the best predictors of overall health. The more aerobically fit you are, the better your heart can pump blood, the longer it takes you to get out of breath, and the farther and faster you’re able to bike or run or swim. One more thing: It also happens to be the form of fitness that helps you live longer and live better by reducing your chances of developing ailments like cardiovascular disease and diabetes. Aerobic fitness is the thing most of us want when we first start working out.

			So how do you build aerobic fitness? For a long time, many coaches and athletes thought that becoming aerobically fit required an enormous amount of exercise performed at a moderate pace. This thinking is reflected in the public health guidelines that generally call for 150 minutes of moderate-intensity exercise per week to derive health benefits. Two and a half hours. At minimum. While this represents less than 2 percent of the total hours in a week, it is a substantial commitment for most people, who cite “lack of time” as their main barrier to exercise.

			The problem with these guidelines is that they scare plenty of people away from exercising. Lots of people are actually incredulous about it—it’s like, you want me to work out for two and a half hours a week? Are you crazy? I can barely manage the laundry! And in fact, only 15 to 20 percent of Americans actually meet those fitness guidelines.

			And yet, the message about how to get fit stayed largely the same: lots of steady-state exercise, which involves moderate activity performed at a constant rate for a prolonged period of time. In part, that’s because people believed there just wasn’t any other way.

			According to the old thinking, sprints were thought to help your sprinting. They were a tool to boost speed—not aerobic fitness. Intervals might help an athlete develop a faster sprint time, but coaches and scientists figured they wouldn’t help much in longer races. Nor would they help much with overall health or fitness. That, at least, was the conventional wisdom in the years before we arrived at our new understanding of the physiology of interval exercise.

			A Fascination with Intervals

			The old line of thinking has changed dramatically over the past ten years, thanks to an explosion of research into the benefits of ultralow-dose exercise. We now know that interval training absolutely can improve aerobic fitness and confer health benefits that we normally associate with substantially greater amounts of endurance training.

			I came to this realization thanks in large part to one of the courses that I teach, a fourth-year elective called the Integrative Physiology of Human Performance. It focuses on the way the body’s various systems—circulatory, respiratory, muscular—work together to meet the energy demand of exercise. Ever since I started teaching the course, my students have been interested in the training regimens of elite athletes. We would discuss everyone from the record-breaking four-minute-miler Roger Bannister to the Tour de France champion cyclist Lance Armstrong (this was before the doping scandal that eventually saw him stripped of his seven victories).

			One training method common to both athletes was intervals—short, hard efforts performed repeatedly. My students found it difficult to understand why intervals would help such athletes as middle-distance runners and road cyclists. After all, the athletes’ specialties very much depended on their aerobic fitness—on their ability to sustain physical activity without getting tired. The students would ask, “How can interval training boost your aerobic fitness when it is such an anaerobic type of exercise?”

			The students’ question was based on a misconception—one that many people have had for a lot of years. It has to do with the body’s aerobic and anaerobic energy systems. I’ll explain this in more detail later on, but for now, just remember that the body has two main ways of powering movement. It draws mostly on the anaerobic system when it requires lots of power, as when lifting heavy weights or all-out sprinting. And it mainly draws on the aerobic system when it performs less-intense movements for longer bouts of time, like jogging or cycling long distances.

			But what about repeated sprints? It turns out that these are particularly taxing on the aerobic system. To illustrate this point to my students, I would show them the following graph, which reflected our evolving understanding of the energy required for repeated sprints. It’s based on research conducted at McMaster in the late 1990s. In the study, subjects performed a series of three all-out thirty-second sprints on a bicycle, separated by four minutes of rest in between.

				[image: ]

			The left panel shows the energy distribution during the first go-as-hard-as-you-can sprint. Most of the energy is derived from the anaerobic system, although the contribution from the aerobic system increases over the course of the sprint. The right panel shows how that pattern changes over the course of the third sprint, with the aerobic system accounting for a greater proportion of the energy. The precise energy distribution depends on many factors, including the duration of the sprints and the recovery periods, and how many work-rest cycles are completed. But the essential message is the same: as you repeat the basic pattern of sprint, rest, sprint, rest, a greater proportion of the energy comes from aerobic metabolism.

			I started to wonder, what if people did only intervals? What benefit would that provide? How would it affect aerobic conditioning? Certainly, there were clues sprinkled throughout the scientific literature. A 1973 study of Swedish military recruits by one of my mentors, the legendary Scandinavian physiologist Bengt Saltin, concluded that physical fitness could be rapidly improved by interval training despite a short time investment. The Japanese researcher Izumi Tabata showed in 1996 that training using brief, intense intervals could substantially improve cardiorespiratory fitness. Two years later, my master’s thesis adviser at McMaster, Duncan MacDougall, showed that training in short, hard intervals could dramatically increase the amount of mitochondria in muscles, the cellular bodies that use oxygen to burn fuels for energy.

			A Life-Changing Study

			So in 2004, with missed workouts leaving me feeling generally overwhelmed, time-pressed, and out of shape, I went into an intense brainstorming session with a handful of talented and enthusiastic graduate students. (Through the years, I’ve had the privilege of working with many such students who have contributed greatly to my research, and whose names are included on many of the papers I’ve published, along with those of my other research collaborators.) I wanted to study the effects of interval training and whether it was a more efficient way to exercise. Could intervals provide all the benefits of a long run or bike ride—in just a fraction of the time? During the brainstorming session, we decided to focus on how little exercise might be able to provide fitness benefits.

			I was up at the chalkboard, writing furiously, while the students and I debated the designs of potential experiments. Envision lots of shouting while the chalkboard grew increasingly dense with graphs and equations, clouds of chalk dust swirling in the air, and you’ll get close to the atmosphere in the room. How many intervals should there be? How long should each one last? How many rest days should come between them?

			We came up with a simple, short, and focused experiment to examine the power of high-intensity intervals. Thanks to the work of our fellow academics, we knew that intervals could boost cardiovascular fitness and the number of energy-producing mitochondria in muscle tissue. But we didn’t know how quickly these adaptations took place, nor did we know how little exercise was required to trigger the benefits. We also didn’t have a good sense of the power that sprints had to improve performance during good, old-fashioned steady-state aerobic exercise.

			The experiment we designed looked at whether a handful of sprints could improve endurance performance. It worked like this: We assessed how long the subjects could pedal a stationary bicycle set to a fixed workload. Then the subjects went off and conducted six training sessions over two weeks.

			The six training sessions conducted by the subjects required them to sprint on a stationary bicycle. The specific protocol is known as a Wingate test (named after the Israeli sports institute where it was developed, the Wingate Institute), which is designed to measure someone’s anaerobic power—the all-out explosive effort necessary to bike, skate, run, or swim as fast as possible. You hop into the saddle and pedal as hard and as fast as you can for thirty seconds against a high resistance. The idea is to go all out. “Go as hard as you can,” I told the subjects. “As if you’re sprinting to save a child from an oncoming car—go that fast.”

			Wingates can be helpful. “If you’ve never done the Wingate-cycle test, let me try to explain what it feels like,” A. J. Jacobs wrote in his Esquire article about interval training. “It feels like your legs are giving birth. It feels like you’ve got an eight-martini hangover in your calves. Your face contorts like a porn star in an AVN-award-winning threesome scene. You emit noises that resemble feedback at a thrash-metal concert. . . . The upside: It’s over in 30 seconds.” Jacobs is exaggerating just a little about how painful Wingates are. But his greater point is sound. You’re supposed to give it your all.

			Our experiment’s eight subjects were the sort of athletic young adults, men and women, who tend to be around McMaster’s Kinesiology Department. They participated in athletic activities in some form a couple of times a week but weren’t involved in any kind of structured training program. The first workout of the study entailed four Wingates, or four rounds of cycling all out for thirty seconds each, with four minutes of rest in between. The training sessions took place in the lab at the Exercise Metabolism Research Group—a wide, low-ceilinged room filled with lots of computers, monitors, breathing tubes, and exercise equipment like stationary bicycles and treadmills. It wouldn’t look out of place in Blade Runner or the science fiction movies of Neill Blomkamp.

			The training sessions were pretty intense. In our write-up of the experiment, we noted that the subjects were “verbally encouraged” during their sprints. That’s a staid depiction of what actually happened. The atmosphere was as loud and enthusiastic as any I’ve seen in a laboratory setting. Rock music blared. As each participant shifted into the sprint, a half-dozen grad students gathered around to offer encouragement: High-volume shouts. Lots of “Go! Go! GO!” and “YOU CAN DO IT!” Then, after the sprint, there were high-fives and pats on the back.

			The most exciting day happened once the two weeks of training were over, when we conducted the final part of the experiment. Remember how, before training started, we asked our subjects to pedal a stationary bicycle set to a fixed workload for as long as they could? Well, now we asked them to do it again. This was the study’s key measurement, where we assessed the potential performance benefit of the sprint-training sessions. I didn’t have any idea how the subjects would perform or even whether there would be any benefit. We were testing the outcome of only six sessions of sprint training. The total time spent exercising in our study was only sixteen minutes. Would the training really do anything for endurance performance?

			One by one, the eight sprint-training subjects conducted their final tests. The lab was quiet as they did. In the interests of objectivity, we didn’t offer our riders any encouragement or feedback for this part. We also tried to keep our expressions blank, so as not to affect the subject’s performance.

			As the results came in, it was difficult to maintain that façade of impartiality. The numbers were crazy. The sprinters had doubled their endurance times. On average, before the training, the eight subjects could pedal the bike for twenty-six minutes until exhaustion. Following the six sessions of interval training, the average time was fifty-one minutes. It was an amazing result.

			That was the moment I grasped how potent sprint intervals were—and how much they had the potential to improve overall fitness. It was incredible: in approximately the time required to do the dishes, these young men and women had doubled their endurance capacity. It was the most remarkable result I’d ever experienced in my lab.

			The sprints changed the subjects’ bodies in other ways, too. We obtained biopsies of their thigh muscles before and after training. The biopsies showed that, after the training, subjects had significantly more mitochondria in their muscles—because a key enzymatic marker, citrate synthase, increased by 38 percent. That matters because mitochondria are the muscles’ powerhouses. We’ll talk more about the physiology of training in chapter four, but in short, more mitochondria mean you can generate aerobic energy more quickly and with less fatigue.

			It was the first time that such low volumes of training had been demonstrated to have such powerful effects. I marveled at the results on a number of different levels. There was something very powerful about going all out. About giving it your best possible effort. These short, intense intervals, a supposedly “anaerobic” exercise, appeared to have some sort of near-magic ability to improve aerobic energy metabolism. I couldn’t get over how little exercise was needed to produce such enormous effects. A doubling of endurance capacity in only six training sessions? With just sixteen minutes of hard exercise? It seemed miraculous. To this day, more than ten years later, I am still amazed by how little interval training you need to boost fitness and health.

			And keep this in mind: We used a stationary cycle for our study for pragmatic reasons, but we figured the results would be the same for any activity conducive to a sprint approach, such as running, rowing, and even stair climbing. And in the ten-plus years that have passed since, this expectation has been borne out.

			One of the top journals in the field of exercise physiology, the Journal of Applied Physiology, published the study on June 1, 2005. It also published a feature editorial that highlighted the significance of the work. The report “reminds us of the ‘potency’ of very intense exercise,” wrote Edward F. Coyle, a University of Texas physiologist and an expert on human performance. “It appears that this is the first scientific documentation that very intense sprint training in untrained people can markedly increase aerobic endurance. . . . In other words, we are reminded that intense sprint interval training is very time efficient with much ‘bang for the buck.’”

			That week, someone from McMaster’s public relations staff called me up and said, “We have ten newspaper and television reporters who want to interview you.” Nothing I’d done to date had ever attracted that sort of attention before. I appeared live on a national morning-news television show. And then the attention snowballed. Ten interview requests multiplied to twenty, and then a hundred. I wasn’t able to respond to all the media calls. My in-box overflowed with email messages. It was just surreal. I remember being overwhelmed by the amount of media attention. That single study ended up setting me on the research path that I have followed ever since.

			The Second Experiment

			After that first experiment, I started incorporating intervals into my own workouts. I was curious to try things out for myself, of course. But it also made sense for me in practical terms. Time was the biggest factor. By harnessing the power of intervals, my workouts required a third of the time they previously had. (Of course, further research would show that intervals could make exercise even more efficient than that.) Although I was only in my thirties at the time, my left knee was showing the degenerative effects of arthritis—the result of a running injury and subsequent arthroscopic surgery when I was twenty-one. So for my own workouts, I favored low-impact activities. My go-to regimen involved cycling on a stationary cycle, an activity that was very conducive to high-intensity interval training.

			The sprints turned out to provide me with benefits besides just the time gains. At the end of our first study our subjects reported that they’d never felt better. I experienced a similar effect. After a few interval workouts I felt supercharged. In fact, the effects were so remarkable that I started thinking about how to quantify them. Just how powerful were they?

			My team and I designed an experiment to find out. Once again, we gathered in a small group for a brainstorming session. Our idea was to directly compare high-intensity interval training with more traditional endurance training. We were moving into uncharted territory here. As far as I knew, no one had ever compared a workout involving a few short, hard intervals with a large amount of steady-state continuous exercise.

			We decided to compare our sprint-training program with a strenuous regimen of moderate-intensity endurance training based on the typical physical-activity guidelines. We recruited twenty people and divided them into two groups, with five men and five women in each group. They were similar to the subjects in our first study: mainly university students who took part in intramural sports and some habitual exercise but who weren’t pursuing any sort of structured training regimen.

			One group was put on a quite rigorous endurance training regimen for six weeks. These subjects rode stationary bicycles five days a week for forty to sixty minutes per day. They cycled at an intensity of 65 percent of their maximal aerobic capacity, which is within the moderate range as recommended in the public health guidelines. The pace was enough to get their heart rate elevated and get them sweating.

			Now for the interval-training group. They also went on a six-week-long training regimen, but one that required much less work and time. It was modeled after the protocol used in our first study. The subjects began by spending a couple of minutes warming up on the exercise bicycle. Then they performed a thirty-second-long sprint. They rested for four and a half minutes, and then they did another sprint, repeating this four to six times. Instead of training five days per week, they trained three days.

			At this point, it’s important to grasp just how little exercise the interval-training group did. Their total weekly time spent working out was only one-third that of the endurance training group. And that’s counting their rest periods, which required our test subjects to cycle at a lazy pace. Really, they just slowly turned the pedals while recovering from the previous interval.

			If you count only the intervals—that is, if you total the time our test subjects were required to perform hard exercise, then our sprinters worked out for just under ten minutes a week. Compare that with the other group’s four and a half hours of continuous moderate-intensity exercise per week. The time the sprinters spent exercising amounts to less than 5 percent compared with the endurance group.

			Another way to compare the two groups is to consider the amount of energy they expended as they pedaled their bikes. We measured the work in kilojoules (kJ), a unit of energy. Our endurance trainers completed 2,250 kJ in a week of training. That is enough energy to keep a 75-watt lightbulb burning for more than eight hours. Meanwhile, our sprinters completed just a tenth of that. They only did about 225 kJ of work per week—enough energy to keep the bulb burning for about fifty minutes.

			How did the results for the two groups compare? Basically, the improvements were the same for every fitness parameter that we measured. That means both groups improved following the training, but we could not detect any significant differences in the extent of the change between the two groups. The increase in aerobic fitness? The same. The increase in mitochondria in the subjects’ muscles? The same. The change in fuel use and, particularly, the subjects’ ability to burn fat during exercise? The same.

			In short, the experiment showed that approximately ten minutes of hard exercise a week boosted overall fitness to the same extent as four and a half hours per week of traditional endurance training. It’s mind-blowing. A tiny bit of sprint training has the same effect on the human body as a whole lot of endurance training—despite a much lower training volume and time commitment.

			So Is It Possible to Get Fit in Just Minutes a Week?

			The answer is an unequivocal yes. Remember those coaches and trainers who thought intervals were only for sprinters? That intervals didn’t do much for aerobic conditioning? They were wrong. High-intensity intervals may be the most potent method we’ve yet discovered to boost cardiorespiratory fitness.

			Under strictly controlled conditions, in experiments that have been published in the most reputable peer-reviewed physiology journals, my lab and others around the world have shown that small amounts of interval training can produce benefits we usually associate with large amounts of endurance training.

			The harder and faster you go, the less time your exercise requires. Go as hard as you can in short bursts, and you can get the benefits of an endurance exercise regimen with less than 5 percent of the time spent in hard exercise, 10 percent of the work expended, and only one-third of the total workout time commitment. To this day, more than a decade after our first experiment, that fact still boggles my mind.

			But if teeth-grinding, face-reddening effort isn’t really your thing, you can still get the benefits of interval training. The harder you go, the more efficient your workout will be in terms of time commitment. If sprinting as fast as you possibly can is not appealing, or not something you are capable of doing, then you can give 90 percent. Or 80 percent. Even interval walking seems to be better than doing the same exercise at a steady-state pace. So long as you vary the intensity, you’ll still derive proportionally more benefit from your workout than the traditional moderate approach.

			In the next chapter, I’ll describe the exciting, exploding science of interval training—as well as the current scientific thinking on how and why a little bit of interval training is able to trigger its remarkably beneficial effects.

			Then we’ll consider the origins of interval training, including a discussion of how some of the greatest athletes in history have employed interval training to conduct world-record-breaking feats.

			Then the real fun begins. We’ll provide samples of interval workouts. I’ll also discuss the psychology of interval training: how to trick your mind and body to blast through the sprints as effectively as possible. And finally, we’ll consider the future of exercise and how we might work out in the decades to come. Let’s get to it!




			The Fat Burner

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			Noting the obesity epidemic, and the fact that many exercise programs lead to little or no fat loss, Australian scientists set out to design a protocol expressly for inactive people that targets fat loss. This is the result: a series of micro-intervals that are superior to conventional steady-state exercise at reducing fat. Another bonus? Recent research suggests people prefer to perform lots of shorter intervals rather than fewer longer intervals, and this study fits the bill.

			Peak Intensity • 6

			Duration • 25 minutes

			The Evidence • The 2012 Australian study on which this protocol is based had subjects conduct the workout three times a week for 12 weeks, resulting in a 15 percent increase in cardiorespiratory fitness and some intriguing body-composition changes. Participants had a 3.3-pound decrease in overall bodyweight, which is really difficult to achieve with exercise alone. Even better, the subjects’ total fat mass decreased by an average of 4.4 pounds. The workout cut abdominal fat by 6.6 percent and trunk fat by 8.4 percent. Keep in mind that this format relies on comparatively easy sprint intervals, with an intensity of only 6. An earlier 15-week study out of the same Australian lab increased the sprint intensity to an all-out rating of 10+, resulting in a decrease in fat mass of 5.5 pounds and an increase in cardiorespiratory fitness by 24 percent.

			Who Should Do It? • The 2012 study featured overweight and inactive young men, while the earlier, more-intense study featured inactive young women whose body-fat percentage was more than 30 percent. But it’s likely to benefit most healthy populations who feel up to trying it. Don’t be scared off by how extreme this workout looks on the graph; with a comparatively easy sprint-intensity level of just 6, it really isn’t that bad. Plus, the sprints are short, at 8 seconds, and the recovery periods of 12 seconds help a lot. Even if you push the intensity levels, this one is less painful and more accessible than you might think on first impression.


					The key to this protocol is figuring out a convenient way to keep track of the 8-seconds-on, 12-seconds-off format. I suggest staging the workout on an exercise bike, for cyclists, or at a track, for runners—and using a traditional stopwatch or an interval-training timer app that can be programmed to provide stop and start alerts. Or if you’re not technologically minded, you could always just count off the seconds in your head.

					Once you’ve got all that sorted, perform an easy warm-up for 3 minutes.

					Go hard at intensity 6 for 8 seconds.

					Rest for 12 seconds.

					Repeat as many times as possible to a maximum of 60 times, or 20 minutes of intervals.

					Perform an easy cool-down of 2 minutes.



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			High-Intensity Engagement

			It’s midday on a Saturday, a fitness studio in midtown Manhattan. The clients arrange themselves into two lines and then, at the trainer’s signal, explode forward and back across the padded turf floor. There’s a bear crawl, a crab walk, frog hops, and high steps—all performed as fast as possible. At various points the trainer tells the clients to perform sets of burpees, push-ups, crunches, and squats. Resting after the first go-round, the clients have already started to breathe hard. By the third, their athletic clothing is dark with sweat. Everyone here looks fit, but this workout is so tough it’s taxing even the best of them.

			The session at Manhattan’s Tone House gym, renowned to be one of the toughest workouts the city has to offer, is based on the principles of interval training. It’s great—for those who can do it. Unfortunately, associating the training protocol with such tough workouts also comes with a major drawback: It prevents a lot of people from accessing interval training’s benefits.

			Mention the term “interval training” and many people envision football players grunting through all-out sprints on some gridiron grass, or ripped fitness enthusiasts leaping into infinite sets of box jumps. They think it’s not for them. I can understand having that sort of reaction. If I didn’t know anything about the exercise method, I’d probably feel that way, too.

			But the stereotype is wrong.

			The fact is, interval training is something that has a lot of variation in it. Sure, it can be hard-core. But it doesn’t have to be. Retirees and heart patients can do one flavor while elite athletes can perform another. The basic idea of varying the intensity of a workout to make it more effective can be used to create programs that increase fitness for people of all ages and lifestyles.

			Anyone in the exercise trade will tell you that one of the hardest things about getting fit is that, sometimes, for people who are just starting out, exercise hurts. You spend your whole life hearing about stuff like the “runner’s high” and how good people feel when they exercise. Then you do it, and darn it if all that doesn’t seem like a lie. Exercise isn’t this friend who makes you feel good. Not at first. Exercise makes you feel like hell. Exercise is a jerk.

			That period goes away—and if you’re using interval-training techniques, it can go away more quickly. In fact, two former graduate students of our program, psychologist Mary Jung and physiologist Jon Little (from the previous chapter), were involved with a study that shows this. Published in 2012 and led by researchers out of Queen’s University (Kingston, Ontario), the study asked young women to conduct a brief fitness protocol four days a week for a month. Each day, the young women ran through a Tabata-style format of twenty seconds on, ten seconds off, repeated eight times for a total workout duration of four minutes. The “on” portion saw the women conducting one of the following bodyweight exercises: burpees, jumping jacks, mountain climbers, or squat thrusts. It was a bit like the Tone House workout actually—except a lot shorter. The whole workout required about sixteen minutes a week. The women improved their cardiovascular fitness to the same extent as another group that performed two hours a week of moderate-intensity continuous cycling. And the interval trainers became stronger, too—improving their performance on strength tests like push-ups and leg extensions, an added benefit that did not occur in the other group.

			More to the point, though, after experiencing the remarkable benefits of interval training, the young women decided they liked it more than they’d expected to. In questionnaires, the young women said they would be more likely to exercise using interval-based workouts in the future.

			The study’s results reflect the way that the first, painful phase of exercise is temporary. When you use interval-training techniques, it lasts just a couple of weeks. In fact, interval training makes that awkward period that coincides with exercise’s beginning as short as possible. It gets you fit faster so that you can begin enjoying exercise sooner.

			We’re not even talking about the most intense flavor of interval training here. Pretty much any type of interval training, which sees you varying the intensity of your effort throughout the workout, is going to benefit you more, and more quickly, than a comparable period of continuous training. You go out for a walk, and you vary the intensity of your effort? That’s interval training, just as much as is the variety that sees the human equivalent of ultrafit rabbits and gazelles powering through spin classes and the sort of circuit-training workouts that happen at Tone House in New York.

			The Weird and Wonderful Thing About Exercise

			Like a lot of people who have researched the science of fitness, I regard exercise as having near-magical properties. We spend billions on research to create pills that improve health. Most of these pills target only one aspect of health, and many have unwanted side effects. Meanwhile, the most powerful intervention possible—exercise—goes comparatively underutilized. I mentioned earlier in the book that only about 15 to 20 percent of the people in the United States, Canada, and the United Kingdom actually get the 150 minutes of moderate exercise a week that the guidelines suggest. That means anywhere from 80 to 85 percent don’t get the recommended amount of exercise, even though it benefits your physical and mental health in all sorts of ways, from helping you live longer to enabling you to live a happier life. Exercise is the best way to push back the effects of aging. It’s the best way to hedge against a decrepit last few years of your life. Want to live an active life until you’re ninety? The best way to promote that is by exercising regularly. And yet so few of us do it!

			That’s a problem. The human lifespan in the developed world has doubled in the last two centuries, and yet human “healthspan,” or the proportion of our lifespan that we are active and healthy, has not kept up, according to a 2015 Journal of Physiology paper lead-authored by the British physiologist Ross Pollock. The consequence? “The years spent with poor health and disabilities in old age are increasing,” Pollock and his coauthors wrote.

			Alan Batterham is an exercise scientist at Teesside University in Middlesbrough in the United Kingdom. He says there’s a perversity to the human relationship with exercise. Humans are lucky that most of the things that are good for us also happen to be programmed into our gray matter. If we need water, for example, the body sends a thirst signal to the brain, and we drink. But no such need-drive relationship exists with exercise, which may be the only activity our bodies require for optimal health that we’re not biologically preprogrammed to carry out. “There is apparently no innate drive to be substantially physically active,” Batterham observed.

			That’s probably because, in ages past, exercise was something we got enough of purely by doing the things we had to do to survive. In fact, as Harvard University paleoanthropologist Daniel Lieberman points out in a 2015 paper, humans evolved a drive to avoid physical activity—to conserve energy when possible. We did that, according to Lieberman, because thousands of years ago, food was scarce, as was the energy that we derived from food. If you were a hunter, then you needed to conserve those calories to use as you sought your prey. If you were a gatherer, you needed those calories for fuel as you wandered about your habitat, searching out grubs, berries, and other sustenance.

			Things are different today. Thanks to the industrial revolution, urbanization, the automobile, and the development of computer technology, most people in the developed world are able to procure their daily sustenance without expending much physical effort. Many times, all that procuring food requires is a walk from the couch to the kitchen. Now, that biological imperative toward rest has created an exercise paradox—that “people tend to avoid exercise despite its benefits,” Lieberman says. Somewhere, we’re aware that our bodies would work better and we’d feel happier if we increased our activity levels. Yet the pace of life is such that most of us feel we just don’t have the opportunity.

			A Rift in Academia

			Physiologists in general tend to be pretty excited about interval training for all the reasons stated above. But the debate among psychologists is more fervent. Opposition to the technique is exemplified by a study written by a psychologist from Curtin University in Perth, Australia. Her name is Sarah Hardcastle, and she specializes in exercise.

			In a 2014 article published in Frontiers of Psychology, Hardcastle argues that sprint interval training, the most time-effective and intense flavor, is too hard for most people to do. “Proponents of SIT [sprint interval training] have focused almost exclusively on physiological adaptations,” Hardcastle and her coauthors note. Then they ask whether a sedentary population “will feel physically capable and sufficiently motivated to take up and maintain a regime of highly intense exercise.” Sprint interval training, says Hardcastle, “is likely to be considered too arduous and may evoke anticipated perceived incompetence, lower self-esteem and potential failure.” The article’s title? “Why Sprint Interval Training Is Inappropriate for a Largely Sedentary Population.”

			Sure, interval training is really effective, Hardcastle says, but for most people it’s too hard—physically and psychologically. She goes even farther than that, however, arguing that “high intensity exercise is likely to evoke negative affect which may lead to subsequent avoidance of further exercise.” In other words, sedentary people will find sprint interval training workouts so unpleasant that the intense physical activity will discourage them from doing other types of exercise in future. That sprint interval training could put them off exercise altogether.

			There are people out there who subscribe to Hardcastle’s argument. Some highly respected exercise psychologists have completely dismissed high-intensity interval training as a mechanism that can affect public health. They just don’t think people are going to do it. The general belief in exercise programming in the United States is that people would prefer to exercise at a low intensity over a long time rather than at a higher intensity for a short time.

			“The problem of sedentary living is large, particularly in the US, and it’s such that people are scared of suggesting interval training,” says Stanford University’s Jeff Christle. “The fitness industry has gotten a hold of this thing, and in the US they see that as a big deterrent. They’re just concerned about ‘Let’s get people moving. Why make it more complicated than that?’”

			In June 2015 the debate flared up again at the annual meeting of the International Society for Behavioral Nutrition and Physical Activity, which that year occurred in Edinburgh, Scotland. Before a crowd of approximately four hundred, in the Pentland Auditorium of the Edinburgh International Conference Centre, psychologist Stuart Biddle of Australia’s Victoria University argued that interval training’s potency was “largely pointless”—because few people would ever do it. The problem isn’t that people don’t have the time for exercise, Biddle argued. Rather, they’re just not making it enough of a priority. To encourage people to make exercise a priority, Biddle said, according to a transcript of the debate published in an academic journal, “we need to boost people’s positive feelings about exercise. Making it harder and more painful”—as he claims interval training does—“is unlikely to do this.”

			As it turns out, however, many people find interval training more enjoyable than conventional exercise.

			A Short Course on the Psychology of Exercise

			I’ve been interval training for a decade now, and I’ve loved it ever since I started. So when I first heard the psychologists’ objections that people wouldn’t do it, I shook my head. To me, intervals are a completely different animal from continuous vigorous exercise. Yes, it’s hard to maintain a strenuous pace for a prolonged period of time. But intervals are different. You get breaks from the toughest part of the exercise, which allows you to recover and makes the hard work seem easier. Intervals keep you engaged, which makes the time feel like it’s going even faster than it is.

			I couldn’t refute the objections of such figures as Hardcastle and Biddle with my own experience, however. So I dug into the research on the psychology of interval training. One of the most interesting studies I found was conducted by a team out of Liverpool John Moores University in the United Kingdom. They published a study in 2011 that examined whether people preferred interval or continuous running. The neat thing about this study, which was conducted with recreationally active men, was that the researchers tried to match the protocols as much as possible—that is, the average exercise duration, intensity, and distance run were the same. The continuous workouts required the men to run at 70 percent of VO2max for fifty minutes—a good, moderate pace. The interval version required the men to run six three-minute reps at 90 percent of VO2max interspersed with three-minute breaks. The workouts also matched in terms of their average heart rate.

			Afterward, the men were asked to rate which workout they enjoyed more using something called the Physical Activity Enjoyment Scale, and to rate the extent they exerted themselves during the workout. The men believed they exerted themselves more during the interval workout—and yet, they rated the intervals as much more enjoyable than the continuous running. The average enjoyment score for the interval running was 88 while the continuous exercise was down around 61. So here was a study that suggested the old supposition—that higher exertion equals less enjoyment, as well as a lower likelihood to continue performing the exercise—didn’t apply to interval training.

			Ah, the naysayers said. That British study didn’t ask the subjects to rate their enjoyment until several minutes after the exercise had ended. To figure out whether people will actually do the exercise, in the wild, you have to ask how people feel while they’re doing the exercise. (The other problem with the British study, critics said, was that its subjects were fit young men who might be more accustomed to exercise and not experience as much discomfort.)

			One Psychologist’s Take

			As an exercise psychologist, Mary Jung was in many ways the perfect person to attack the problem of interval training’s likability. I got to know Jung when she was a master’s student in our kinesiology graduate program at McMaster. At the time, she was working in the next lab over, studying how to best encourage dieters to stick with their eating plans. Even through the lab’s steel doors and the cinder-block walls, Jung recalls how she would hear us clapping and cheering on our experiment subjects through the course of their training interventions. (We were working on one of our all-out sprint studies at the time.)

			So she came over to check us out. She got one look at a test subject working as hard as she could on an exercise bike, with the music cranked and everyone gathered around to watch. Jung didn’t have any idea what we were doing, she would recall later, but she wanted to be a part of it. And as time went on, at my lab and others, Jung applied a psychological viewpoint to the study of interval training. Her work examines how much subjects enjoyed interval training—and whether they would continue the training method in future.

			Jung’s interest in the psychology of exercise far predates her time as a graduate student. In high school, she started teaching fitness classes and continued for sixteen years: spin classes, aerobics, step classes, boot camp workouts, kickboxing—you name it, she taught it. She also has more than a decade’s experience as a personal trainer. You know, in addition to her PhD in exercise psychology. She currently runs the Health and Exercise Psychology Lab at the University of British Columbia’s Okanagan campus, where her research interest resides at the intersection of exercise and psychology. For example, she investigates how it is that some people develop great exercise habits while others resent having to walk to the corner store to buy snack food. Why do some people stick with workouts while others can never keep to their routine for longer than a week or two?

			Back in 2013, Jung encountered critics claiming that the various iterations of interval training were too difficult to conduct, and she got a little frustrated. She’d witnessed firsthand how people enjoyed the variety and potency of high-intensity interval training. Not only did Jung know that other people liked HIIT workouts; she herself has participated in and enjoyed HIIT. “I like how quickly it works,” she says. “And I can see how others respond to that, too. Using HIIT, they notice the changes brought on by exercise a lot faster and a lot earlier once they start working out.”

			Jung became as hopeful about interval training’s potential to affect public health as I was. She, too, regards it as a way to bring the benefits of exercise to more people—because interval training’s reduced time commitment will eliminate the barriers that prevent people from exercising. And she’s witnessed firsthand people’s sense of pride and accomplishment after they’ve done a particularly rigorous interval workout.

			Jung believes that interval training is peculiarly suited to healthy but sedentary people just beginning exercise regimens. “What is considered high-intensity for an individual who has not exercised in years looks drastically different than conjured-up notions of all-out exercise performed by athletes and in boot camp classes.” Someone who is completely out of shape could gain the extra-potent benefits of interval training, Jung believes, purely by walking up a slight hill, turning around to go back down, and repeating that a handful of times.

			“There is a perception among people, particularly among those who don’t exercise regularly, that interval training is not for them,” Jung says. “But many people don’t understand what interval training is. They have visions of these Army-style boot camp workouts. They ask, isn’t HIIT only for elite athletes? And that perception may be keeping the benefits of interval training away from the people who could most use the benefits.”

			The Comparison Study

			The next step for Jung was to conduct a scientific examination that compared how beginner-level exercisers felt during HIIT and during moderate continuous exercise. It was one of the first times an investigator had looked at this particular facet of HIIT. Jung aimed to make the study as realistic and practical as possible. Through posters at the Okanagan campus, she and her fellow researchers recruited forty-four young people who were not exactly sedentary but certainly not athletes either—people who worked out less than twice a week. Then she asked them to conduct three different workouts.

			The first was a moderate-intensity continuous bout on an exercise bike that lasted forty minutes, saw them working out at 40 percent of their maximum power output, and raised the subjects’ average heart rate to 69 percent of their peak. A second was a vigorous intensity continuous workout that saw them working out for twenty minutes at 80 percent of their maximum power output, which raised their average heart rate to about 89 percent of their peak. And the third was the interval workout. For this study Jung used the Ten by One protocol that we had used for less athletic subjects, such as sedentary people and those with diabetes.

			At various points during and after the three workouts, the subjects were asked to rate how they were feeling. Then, twenty minutes after they finished, the researchers asked them how likely they would be to engage again in the type of workout they’d just completed.

			According to their own ratings on an 11-point scale, the subjects felt good during the continuous moderate exercise, just OK during HIIT, and pretty bad during the continuous vigorous exercise. But one of the most interesting things about the study was the improvement in the subjects’ self-rating that occurred twenty minutes after the HIIT workout. Jung calls this the “positive rebound effect.” In other words, twenty minutes after the workout was over, all three groups felt much better than they had during the workouts—but the moderate and interval groups felt the best.

			Next, asked to rate their likelihood to engage in any of the three workouts in the future, the subjects said they were equally likely to conduct continuous-moderate and interval-training workouts, while they were less likely to conduct continuous vigorous exercise.

			Jung and her coauthors then surveyed the group about which activity they had most enjoyed. HIIT was ranked as slightly more enjoyable than the moderate exercise, which in turn was rated as more enjoyable than the vigorous exercise.

			Finally, when asked to name an exercise choice as their favorite, the subjects said they far preferred HIIT. Twenty-four of them identified intervals as their favorite exercise, while thirteen preferred continuous moderate exercise, and four preferred continuous vigorous exercise. (Presumably, the remaining three indicated no preference.)

			So the subjects felt just OK while they were doing the HIIT workout—but then overwhelmingly chose it as their favorite? Does that make sense?

			Mary Jung believes it does. The interval approach, she says, “breaks down the exercise sessions into short, surmountable bursts, potentially allowing for multiple successful experiences.” In other words, when the subjects completed a sprint, they felt as though they’d accomplished something. And that sense of accomplishment offset the discomfort of the more strenuous interval. The workout made them feel like exercisers—a feeling they’d never had before. In addition to that, factor in the time savings. Taken together, that’s all enough to justify why the subjects favored interval training so much more than the other two workout forms, according to Jung.

			Jung believes—and I agree with her—that her study shows that people are more sophisticated than some exercise psychologists believe.

			The old thinking, which suggests that most people aren’t likely to perform difficult exercise, doesn’t seem to apply to interval training. Not that intervals have to be all that difficult. The most strenuous versions of interval training require you to push it. When you’re starting out, that can hurt. And what Jung’s study shows is that people take in the time-efficiency benefits of HIIT, factor in the boost of confidence that happens after they complete an HIIT workout, and then also consider the fact that interval workouts tend to be less boring than conventional endurance training—and they weigh all that against the temporary discomfort they experience while doing a short interval. And they decide that HIIT is worth it.

			Jung has also demonstrated that people prefer HIIT for yet another reason. She’s spent the past several years following sedentary and diabetic individuals through interval-training programs. While lots of people are doing that, it’s the way that Jung designs these workouts that makes them significant. In the usual template, she asks a certain subgroup of the population to perform a fitness training program—some pursue moderate continuous exercise; others pursue interval training. Then Jung sits back and waits. Weeks or months can go by, depending on the study. And once some time has passed, she checks in with the group to see who still continues to exercise. The point is to conclude which sort of workout sets up people to exercise regularly in the future. To increase that proportion of people who do get the activity the guidelines suggest well beyond 15 to 20 percent.

			For example, in 2015, in the Journal of Diabetes Research, Jung and her coauthors published a study that followed twenty-six adults through one of two twelve-day exercise programs, one featuring only intervals, the other featuring moderate-intensity continuous exercise. These were middle-age adults who were pretty out of shape and qualified as prediabetic. The moderate group could manage only twenty minutes of continuous exercise at a time and gradually worked their way up to fifty minutes. The interval group could manage only four one-minute intervals separated by a minute’s rest, and over the course of the twelve days they worked themselves up to our standard Ten by One workout. Then Jung and her group left the subjects alone for a month.

			When they checked in with the subjects again after the month had passed, they found that the interval-training group was a lot more likely to perform vigorous exercise on their own than the group who had conducted moderate-intensity exercise. In fact, a month after the training program ended, the interval group was doubling the amount of vigorous exercise they’d conducted previously. A similar study, which was not yet published while I was researching this book, reveals analogous results after six months.

			So what’s going on? Jung believes that interval training is more effective than moderate-intensity continuous exercise at selling people on the benefits of exercise. She says, “From a psychological perspective? For people who have spent most of their lives avoiding exercise because they think it isn’t for them? They go through an interval-training program, and they get this massive boost in confidence. It’s like, ‘Oh my gosh, I did it.’ They think to themselves, ‘I may not be an athlete, but I really worked it.’ They get a sense of accomplishment. You don’t get that same rush from walking around the block at a moderate pace. And from an exercise-adherence perspective? That confidence is really important.”

			There’s also the fact that physical changes happen sooner in people who do interval-training workouts than in those pursuing moderate-intensity continuous training. Stairs become a lot easier to climb. In general, they just feel better, faster, with interval training. “They’re happier with the results,” Jung says. “That elicits a good vibe, good feelings, pride. When you feel that, you kind of want to feel that again. And you talk about it at parties—‘Hey, I’m an exerciser now.’”

			A Few Words for Those Just Starting Out

			First, remember that interval training has a lot of different flavors. You can enjoy its benefits simply by varying the intensity of an aerobic workout. You push hard, you back off, you push hard again. Congratulations. You’ve just performed the same sort of workout that’s been used by Olympians and world-record holders.

			I believe interval training is perfectly appropriate for beginning exercisers to do. And I believe that because of the way that sedentary people tend to work out when they first start exercising. Allow me to explain.

			Mary Jung and Jeff Christle both have led studies that have asked sedentary populations to conduct exercise—the sort of subjects who some believe should run away screaming from interval training. Jung has worked with diabetics as well as obese and sedentary people on the verge of metabolic syndrome; Jeff, with people who have had heart failure. And both Mary and Jeff say the same thing.

			People who are deconditioned—completely out of shape, perhaps because of cardiovascular disease or an unhealthy lifestyle—might set out to conduct moderate-intensity continuous exercise. But whatever they tend to do, they have to take rest breaks. No matter how moderate the exercise, they can’t keep at it for long.

			Bear in mind, some of these people get out of breath going up a flight of stairs. They can’t walk all the way around a block in one go. But let’s say they try. Let’s say something has happened to motivate them: A close friend has had a health scare. Or their doctor has asked them to follow the 150-minutes-per-week-of-activity guideline, and so they set out for a walk. And they can’t do it. They can barely get two lampposts down the street before they have to take a break. And that turns out to be a big buzzkill. They berate themselves because they weren’t able to manage the continuous exercise. And they end their attempt at moderate, continuous exercise by feeling bad about themselves.

			But what if we took a different approach? What if we told these people, “Hey, listen. Don’t beat yourself up because you weren’t able to do a certain amount of moderate continuous exercise.

			“Instead, celebrate yourself, because you know how that bout of walking just elevated your heart rate so much that you got completely out of breath? You just did an interval! And after you take a break, and you walk the two lampposts back to your house? That’s another interval. Two intervals—good going! You’ve just done an interval workout!”

			The people who dismiss interval training as too complicated and too arduous lose sight of the fact that most deconditioned people—the people they most want to reach—end up starting out accidentally conducting interval training anyway.

			They do it naturally. They set out for a walk, get a ways, take a break. Then they go a little farther, take a break. They head back, go a ways, take a break.

			Interval training also seems more manageable to these folks. Let’s say you set them up on a protocol that has been shown to work great for various populations: the Ten by One, which asks people to work hard for a minute, then back off, and repeat that ten times for a total of twenty minutes per workout. Ask people to do it three times a week for a total duration of an hour? That becomes a lot more manageable—particularly to the sedentary target population that US public health officials most want to reach.

			“Using intervals to get people through the door is a nice way to get sedentary people moving because you benefit so quickly,” says Jeff Christle. “Intervals three times a week, the Ten by One—I think that [with that] kind of program, within four weeks they’ll see really nice improvements. With a regular walking program, the improvements take twice as many weeks. That’s one of the big advantages [of interval training].”

			In the next chapter, I map out a series of workouts for everyone from older people who have never exercised to high-performance athletes looking to gain an edge in their next race. But before we get to that, I want to finish this chapter with some tips. The hardest thing about interval training is starting out. Particularly after you’ve just begun an interval training protocol, the more-intense sprint portion of the workouts can be tough. But here are two tips to make them more enjoyable—or at least, hurt less.

			First, music helps. A 2015 McMaster paper I coauthored analyzed how distraction affected sprint workouts. We found that listening to the motivational music of their choice helped our subjects pedal harder and faster than not listening to any music at all. The idea is to get amped up, to psych yourself into a state that makes it easy to reach the high intensity. Some people use dance music; others, gangsta rap or punk rock. For me, old-school Van Halen does the trick.

			Second, get a little help from your friends. Whether it’s a buddy shouting, “Go! Go! Go!” or a coach applauding your effort, encouragement helps as much during intervals as it does for anything else. At least, that’s the take of a 2013 study out of Western University that examined how verbal encouragement affected enjoyment of an interval workout. When compared with groups who received little or no encouragement, those who got positive feedback during their sprints ended up enjoying their workouts more. After all, some workouts can be tough—so take all the help you can get.

			Now, I’d like to present Mary Jung’s five tips for starting and sticking with an exercise program.

			1. Boost Your Confidence

			Developing the confidence to begin exercise can be a chicken-or-egg situation, Jung says. To start out, you have to have the confidence that you can do it. But how do you develop that confidence if you’ve never done the exercise in the first place? To solve the problem, Jung turns to the work of renowned Stanford psychologist Albert Bandura, who determined some of the most effective ways to develop a belief in oneself. Say you want to start a minute-on, minute-off workout but you’re not sure whether you can push yourself for a minute. Think about other times you’ve broken a sweat; maybe you recently had to run to catch a flight in an airport. Apply that feat to this new situation. “I sprinted to the gate and caught the plane to La Guardia,” you might say. “And if I can do that, surely I can do this.”

			Another way to develop confidence is to look at the stories of other people who have been through what you’re about to go through. Throughout this book we’ve discussed how cardiac rehab patients and those with type 2 diabetes have started and stuck with interval-training workouts. If they can do it