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An illustrated guide to the core design principles of the body’s musculoskeletal system—for kinesiologists, movement therapists, yoga teachers, dancers, and bodyworkers of all kinds

What does knowledge of anatomical structure have to do with preventing everyday muscular aches, pains, and injuries? According to Dr. Theodore Dimon, everything!

Our bodies are designed to work holistically, supported by an intelligently organized system of muscles, bones, and connective tissue. So when we target problem spots by stretching, relaxing, or strengthening individual muscles, we bypass the dynamic, interconnected network that enables healthy functioning and injury prevention. Understanding how this system works in action is the key.

In this groundbreaking guide, Dr. Dimon describes the basic principles that govern our bodies’ musculoskeletal architecture and provides practical exercises to activate specific muscle groups and demonstrate our bodies’ efficient holistic function.
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			 				Title Page



				Introduction: The Key to Our Human Anatomical Design 					 						“Physician, Heal Thyself!”

						Beyond Healing, Treatment, and Cure


				1: The Musculoskeletal System and Its Dynamic Design 					 						The Body in Action

						The Dynamic Role of Muscle

						The Body’s Tensegrity Design

						The Contractile Function of Muscle

						The Second Function

						Proprioception and Muscle Length

						The Central Role of the Head and Spine

				2: How the System Works 					 						1. Each system has a functional design.

						2. Length is a key principle of muscle function.

						3. Muscle groups function in the context of upright support.

						4. The relationship of the head to the trunk is the key organizing principle.

						5. The key to the part is the whole.

						6. The parts influence the whole.

						7. Many systems, one response.

						How the Chapters Are Organized

				3: Extensors and Head Balance 					 						The Lengthening Back


						The Extensors

						Dynamic Muscle Length and Head and Spine

						The Extensors of the Legs

				4: Flexors and Front Length 					 						Key to the Flexors


						The Flexors

						The Flexor Line

						The Flexors and Head Balance

				5: Lengthened Support and the Healthy Spine 					 						Length: The Key to the Spine


						The Spine

						The Spinal Curves

				6: The Spiral Musculature of the Trunk 					 						Key to the Spiral Musculature


						The Spiral Lines

						Tracing the Spiral Lines: How the Oblique Layers Form a Double-Helix Spiral Pattern

						The Human Architectural Marvel

				7: Breathing 					 						The Key to Breathing


						How We Breathe: The Ribs and Diaphragm

						The Anatomy of Breathing

						The Joints of the Ribs

						The Action of the Ribs

						Intercostal Muscles

						The ; Diaphragm

						Breathing and Upright Support

				8: The Larynx and Throat 					 						The Key to the Larynx and Throat


						The Suspensory Muscles of the Larynx

						The Flexor Sheet of the Throat

				9: The Shoulder Girdle 					 						Widening the Shoulders


						The Shoulder Girdle

						The Naturally Widened Shoulders

				10: The Arms 					 						The Key to the Arms


						The Upper Limb

						The Spirals of the Arm

				11: The Hips 					 						The Key to the Hips


						The Pelvic Girdle

						The Iliopsoas Complex

						The Gluteal Muscles

						Muscles of the Hip Joint: The Deep Six

				12: The Leg Spirals 					 						The Key to the Leg Spirals


						The Leg

						A Tale of Two Spirals

						Tracing the Leg Spirals

						The Tendons Acting on the Foot

						The Lower Leg and the Transverse Joint of the Foot

				Appendix 					 						“Directing” and the Postural System

						The Principle of Non-Doing

						The Semi-Supine Position

						The Primary Directions

						Kinesthetic Thinking: The Key to Directing

						Wishing, Attending, and Non-Doing

						The Concreteness of Thinking

						Directing and Antagonistic Action

				Endnotes 					 						Chapter 1

						Chapter 2

						Chapter 3

						Chapter 5

						Chapter 6

						Chapter 8



				Photo Credits

				About the Author

Anatomy in Action

The Dynamic Muscular Systems that Create and Sustain the Moving Body

				By Theodore Dimon, EdD

				With illustrations by G. David Brown

				Foreword by David I. Anderson, PhD

		 			Copyright © 2021 by Theodore Dimon. All rights reserved. No portion of this book, except for brief review, may be reproduced, stored in a retrieval system, or transmitted in any form or by any means—electronic, mechanical, photocopying, recording, or otherwise—without the written permission of the publisher. For information contact North Atlantic Books.

			Published by

North Atlantic Books

Berkeley, California

			Cover art and illustrations by G. David Brown

Cover design by G. David Brown and Jasmine Hromjak

Book design by Happenstance Type-O-Rama

			Anatomy in Action: The Dynamic Muscular Systems that Create and Sustain the Moving Body is sponsored and published by North Atlantic Books, an educational nonprofit based in Berkeley, California, that collaborates with partners to develop cross-cultural perspectives; nurture holistic views of art, science, the humanities, and healing; and seed personal and global transformation by publishing work on the relationship of body, spirit, and nature.

			North Atlantic Books’ publications are distributed to the US trade and internationally by Penguin Random House Publishers Services. For further information, visit our website at

			MEDICAL DISCLAIMER: The following information is intended for general information purposes only. Individuals should always see their health care provider before administering any suggestions made in this book. Any application of the material set forth in the following pages is at the reader’s discretion and is their sole responsibility.

			Adapted chapter from Neurodynamics: The Art of Mindfulness in Action by Theodore Dimon, Jr., published by North Atlantic Books, copyright © 2015 by Theodore Dimon, Jr. Reprinted by permission of the publisher.

			Library of Congress Cataloging-in-Publication Data

			Names: Dimon, Theodore, Jr. author.

Title: Anatomy in action : the dynamic muscular systems that create and

sustain the moving body / by Theodore Dimon.

Description: Berkeley, California : North Atlantic Books, [2021] | Includes

bibliographical references and index. | Summary: “A guidebook

illustrating the principles behind the body’s musculoskeletal system”—

Provided by publisher.

Identifiers: LCCN 2020036965 (print) | LCCN 2020036966 (ebook) | ISBN

9781623175801 (trade paperback) | ISBN 9781623175818 (ebook)

Subjects: LCSH: Musculoskeletal system—Anatomy. | Human locomotion.

Classification: LCC QM100 .D558 2021 (print) | LCC QM100 (ebook) | DDC


LC record available at

LC ebook record available at


			I have admired Ted Dimon’s work since I read one of his earliest books, The Elements of Skill: A Conscious Approach to Learning, many years ago. My admiration and enthusiasm for his work only increased after I read this latest book. The book is an important contribution to the literature and it has the potential to positively impact the field of human movement science as much as the profession of Alexander Technique teaching. Moreover, it offers a practical self-help guide to the countless numbers of people who seek a means for dealing with the myriad of maladies that result from chronic stress and tension.

			I write this foreword several months after the start of the COVID-19 pandemic. The human species has experienced multiple pandemics over millennia, but one is particularly relevant to the subject matter of this book. It is the pandemic of musculoskeletal ailments that besets modern humans; a pandemic that may have started when our ancestors transitioned from hunter gatherers to farmers some twelve thousand years ago, but which was certainly exacerbated and accelerated by the start of the industrial revolution just over 250 years ago. F. M. Alexander argued convincingly that modern civilization was responsible for much of the physical deterioration observable in modern humans. Through systematic self-observation and experimentation, he developed a technique to address this deterioration. As proponents of the technique know, it is a reeducational technique rather than a therapeutic technique, treatment, or cure. It rests on the premise that specific problems in the musculoskeletal system can be understood and addressed only in the context of how the system operates as a functional whole. It stresses the importance of the dynamic relations among the parts of the system, not the least of which is the dynamic relation between the head, neck, and back in determining the integrated functioning of the whole system.

			Alexander taught us that a generalized expansion of the musculoskeletal system characterizes effective and efficient movements. Such expansion is particularly apparent in a lengthening and widening of the torso and in the forward and upward movement of the head relative to the spine. He did not, however, have an anatomical or physiological explanation for why lengthening and widening was so fundamental to movements, though he was masterful in bringing about such lengthening and widening in his pupils. This is where Ted Dimon makes his primary contribution. He advances a theory of how the musculoskeletal system works that not only clarifies many of the teaching procedures in the Alexander Technique, but also challenges scientists to think about human movement in a new light. The theory builds on the principles of systematic self-observation and experimentation advocated by Alexander and draws on decades of experience teaching the Alexander Technique as well as recent scientific advances in our understanding of human biology.

			 				Contemporary anatomy books provide detailed descriptions of bones, articulations, ligaments, and muscles in a mechanistic and reductionist manner. Yet they fail to explain how the entire collection of components that make up the musculoskeletal system has evolved to function as a coherent whole. These books privilege understanding the parts over understanding the whole, perhaps because we have such a poor understanding of what binds the parts into the whole. Anatomy in Action takes a very different approach. Ted Dimon contends that the musculo-skeletal system can be understood only in the context of its function to provide upright support. That support is not simply supplied by the bones, as is often taught to students of anatomy, but instead is a function of the dynamical relations between all of the components that comprise the musculoskeletal system, including bones, muscles, and the entire network of connective tissue. Counterintuitively, Ted Dimon argues that a critical contribution to the integrity and stability of the system, as well as to heightened proprioceptive awareness, is the muscles’ capacity to lengthen between their bony attachments. When the system functions the way it evolved to function, movements are light and effortless. When we interfere with that natural functioning, problems arise. These ideas are sure to cause a buzz in the scientific community and cause many to rethink the merits of the traditional and contemporary corrective exercise approaches to improving musculoskeletal functioning and human performance.

			 				A lucid description of how the parts of the musculoskeletal system relate to the whole and how the whole in turn affects the parts is not the only contribution Anatomy in Action makes to our understanding of human movement. Equally important are the clear and concise step-by-step procedures for restoring the integration between the parts and the whole. The rationale behind the procedures, many of which will be familiar to teachers of the Alexander Technique, becomes obvious when viewed in the context of the theory of musculoskeletal functioning advanced in this book. Moreover, the procedures reveal it is possible to treat the root causes underlying musculoskeletal system dysfunction rather than just the symptoms associated with such dysfunction.

			This book is beautifully illustrated and replete with photos, diagrams, and examples that highlight and clarify its contents. Ted Dimon’s latest work is a valuable resource for anyone who seeks to relieve muscular tension, restore lost function, improve coordination, or achieve peak performance for themselves or others. It is also a wonderful read for anyone who is curious about how modern humans can effortlessly control an amazingly complex body by thinking clearly about its natural design. I will consult this book frequently in my own work!

			David I. Anderson, PhD

			Director, Marian Wright Edelman Institute for the Study of Children, Youth and Families, San Francisco State University and Professor, Department of Kinesiology, San Francisco State University


The Key to Our Human Anatomical Design

			Few people today, it seems, are free from joint, back, or muscle pain. With our increasingly sedentary way of life, these problems are bound to become worse. Children, generally speaking, are free from musculoskeletal problems, but huge numbers of adults in today’s stressful world live with musculoskeletal difficulties of one kind or another.

			To a large extent, these problems can be attributed to our modern lifestyle, coupled with the distinctly human upright posture that has made this lifestyle possible. The spine of a four-footed animal is oriented horizontally and supported by fore and hind limbs. To produce upright human posture, the trunk must be brought directly over the hind limbs, which gives us a generally unstable form of support that is prone to various forms of collapse. This upright posture also requires the development of a lumbar curve, which makes the lower back highly unstable and vulnerable.

			Given this scenario, it seems we must do one thing if we want to overcome tension problems: balance faulty postural habits by removing tensions and compensating for the weaknesses associated with these imbalances. Today, dozens of methods are designed to do just that—virtually all of them based on the premise that our posture is faulty and must be corrected.

			 				As I will show in this book, however, this approach tells only part of the story. Our upright posture is amazingly subtle and complex. The notion that “if something goes wrong, we must correct it” completely overlooks the capacity of the body to function naturally and healthfully. Why, for instance, do most young children, and even some adults, exemplify perfect coordination and muscle tone, without exercise or intervention of any kind? The answer is that, when working properly, the body is designed to function in a balanced and effortless way and, furthermore, is designed to function this way at a completely automatic level when not interfered with. To properly treat the problem, we need to understand how the muscular system is designed to work, because therein lies the secret to how we can function normally and healthfully.

			Instead of understanding this design, however, we rush to correct the problem by massaging, stretching, releasing, or treating muscles. If, for instance, we experience pain while sitting, the usual assumption is that muscles are working incorrectly and that we must correct these imbalances by strengthening muscles or balancing the activity of opposing muscle groups. This approach, however, treats symptoms and only superficially addresses the real problem. If, instead, we take time to examine and restore our natural ability to sit, we will not only be able to sit easily and effortlessly, but in the process, we will reinstate natural and automatic changes in muscular and reflex functioning that are far deeper and more meaningful than what we can achieve through corrective exercise, treatment, or massage.

“Physician, Heal Thyself!”

			When we suffer from musculoskeletal difficulties, we usually assume that something is wrong with the body and, in response, seek the help of professionals—massage therapists, physical therapists, and so on—who possess objective knowledge about the body and how it works. The ability to cure disease based on objective study of the body is the foundation of the biological and medical sciences. If I am suffering from an infectious disease, I go to a doctor who has the knowledge and experience to identify and treat the disease based on the study of this disease and the forms it takes. In somewhat similar fashion, various experts are trained in the diagnosis of posture, muscle function, and exercise physiology based on the clinical study of patients and ways of treating them.

			As I will show in this book, however, muscle tension cannot be diagnosed or treated in the same way that medical scientists study disease. If, for instance, you are suffering from lower back tension, a physical therapist or massage therapist may be able to identify and treat tight muscles and, in this way, provide therapeutic relief. But the solution to tight muscles—which, after all, does not constitute a medical condition in the normal sense of the word—is to restore the lengthened working of muscles based on an understanding of the coordinated working of the back and related muscles. No amount of treatment can produce this condition, which requires knowledge of how the back works, how to bring about length in muscles, and how to coordinate the body in action. As I will show in this book, this kind of knowledge requires a new paradigm and new ways of looking at the body and how it works.

			This is not to say that clinical diagnosis and medical treatment are never warranted in musculoskeletal problems. If you woke up this morning with shooting pains in your shoulder and arm, it would be not only reasonable but advisable to find someone with the medical and clinical expertise to identify the specific problem and, if necessary, to treat it. Symptoms such as these suggest that something is wrong, and when something is wrong, you need to go to the appropriate expert. But muscle tension as a general problem belongs to a different category of function and requires a new kind of knowledge about the coordinated working of the musculoskeletal system and the ability to coordinate muscles based on this knowledge. This kind of knowledge cannot be gained through objective or clinical observation alone, any more than the anatomical study or dissection of the larynx can teach us to command the proper use of our voice.

Beyond Healing, Treatment, and Cure

			Belief in treatment and cure is deeply embedded in our ways of thinking about and approaching the human body. If something is wrong—or if we think something is wrong—we want someone to tell us what the problem is so that it can go away. In such cases, we rely on the authority of experts who have specialized knowledge of the disease in question. Such an attitude may be warranted when we are ill and require treatment, but it is not nearly as appropriate in addressing muscular tension. In this case, we must understand how the body works in a positive way and how to bring about these improved conditions on our own through a process of education and self-study. Forms of treatment not only fail to provide this knowledge but, even worse, reduce the subject to being a passive recipient of treatment. This is true even of holistic techniques, many of which, in the name of education, treat symptoms without imparting real knowledge to the subject about how the body works and how to perform actions in a more balanced and conscious way. To be valid, a system of kinesthetic education must be based on principles that can be learned by a motivated student, that can be applied in a meaningful way to daily activity, and that lead to ongoing insight and knowledge about the body and about oneself. This kind of know-how requires a new kind of science based not on forms of treatment but on observation and knowledge of the living organism in action.


			My own exploration of this subject began many years ago, when I injured my back in college. While stretching after a workout, I felt a twinge and, soon afterward, my back went into spasm and I was immobilized for several hours. I thought I had simply pulled a muscle but, within a few weeks, the spasms were happening every few days. I assumed that, because I had done a lot of strenuous exercise, my muscles were too tight, so I tried a number of methods for reducing tension—relaxation, stretching, yoga, meditation—but to no avail. Even when my muscles were relaxed, I noticed that, once I resumed normal activity, the problem returned. I began to suspect that I was doing something harmful and began to explore kinesthetic methods that would heighten my awareness of what I was doing in action.

			 				One such method had been developed by F. Matthias Alexander, an Australian actor who discovered that his own vocal and breathing difficulties were caused by a harmful pattern of tension that interfered with how his body was designed to function naturally.1 Based on his observations, he developed a practical method for helping people notice and prevent these tensions. I began having lessons in the Alexander Technique and found that my back problem was connected with harmful tensions in my back and legs and that, by paying attention to these tensions, I could get some relief. Wanting to learn more, I began to train full time in the Alexander Technique and, within months, began to experience periods where the tension was entirely absent but would return when I succumbed to my old habits. It soon dawned on me that nothing had been wrong with my back and that my problem had been caused by unconscious habits that interfered with the natural functioning of my muscular system. Interested now in the subject as a whole, I went to graduate school, where I began to explore the problem of performance, habit, and action as a new subject in educational development. I also wanted to introduce the subject of awareness in action as a new field of study, to start an institute, and to train teachers in the new field.

			To do this, however, I needed to clarify various aspects of the subject on which these views were based. First and foremost was the notion that the body had a natural design—a claim for which I had little evidence or support. If, for instance, you look at anatomy books, they can tell you a lot about particular muscles, but how the parts relate to one another—or whether an overarching design principle explains how the parts organize as a whole—is completely omitted, as if the body works in parts and the whole is simply the sum of these parts. Yet clearly there was a connection between body parts—one that provided the key to how muscles and the musculoskeletal system work as a whole. When I began training teachers, I observed the coordinated working of this system every day in my students. Yet clear as this knowledge was to me at an experiential level, I could not account for it in a concrete and coherent way.

			 				The breakthrough came when I realized that muscles function on the basis of length. The usual views are that muscles contract to produce movement and support and that if muscles are tight or shortened, they can be stretched, massaged, or released but cannot actually lengthen. What these approaches missed is that, to support the skeletal framework, muscles are actually lengthened between their bony attachments—a concept that is completely counterintuitive because muscles that are lengthening (and not eccentrically contracting) cannot support anything. And yet this is what I actually observed in people: muscles produce support not by shortening but by lengthening—a quality in muscles that seems to function not simply as a remedy for tight muscles but as a fundamental principle in nature. Based on this, I developed a theoretical model for how the musculoskeletal system works—or what I called the postural neuromuscular reflex (PNR) system—that included muscle length, muscle tone, and the organizing relationship of the head and trunk. The description of these elements, and how they function as a whole, became the foundation for my book Neurodynamics,2 in which I lay out a basic theory and practice of the control of the organism in action.

			Having established this theoretical model, however, I realized that I still had not described in detail how the musculoskeletal system worked. I knew, for instance, that the shoulders are normally shortened and narrowed and, for the system to work properly, they need to widen. This involved releasing the flexor muscles that cause the narrowing, which requires a process of paying attention to the muscles and giving them time to release. But I now realize that it is possible to go much further than this. As a system, the shoulders have a definite design, and each of the components of this system—the flexors in front, the extensors in back, the rotator cuff muscles—participates in this larger system in a clearly defined way. The same is true of the musculoskeletal system as a whole, which is made up of a number of subsystems that can be described in detail.

			 				The description of these systems, which I began as an exploratory project but which has since become increasingly concrete and defined, is the basis of this book. Various methods offer to cure or treat various problems in the body without addressing the much more fundamental question of how the body is actually designed to work. As I worked on this project, I began to lay down a detailed anatomical description of each system and how it works. This begins, as we will see in Chapter 1, with a review of the basic theory of musculoskeletal function (the PNR system) and, in Chapter 2, with an explanation of how this theory applies to the different systems in the body. In subsequent chapters I look at the specific anatomical systems—extensors and flexors, the shoulder girdle, the upper limb, and so on—and describe in detail how each works. In this way, I not only show that we possess a naturally coordinated musculoskeletal system, but I describe how each of these systems contributes to the working of a coordinated whole. Having now worked with thousands of people over nearly four decades, in practice I have seen how each of these systems can be restored, based on a working knowledge of their dynamic design and how to restore it. Neither the identification of postural faults nor forms of exercise and treatment are substitutes for practical knowledge of how these structures work as a coordinated, dynamic system.

			It is my hope that my present work, in describing this system in detail, will contribute to a practical and theoretical understanding of this vital subject and to an advancement in our knowledge of the remarkable and subtle workings of that greatest of all instruments, the human body.


The Musculoskeletal System and Its Dynamic Design

			Although it is an obvious fact that muscles produce movement, how the musculoskeletal system works as a coordinated whole is far less clear. Although we are all familiar with the idea of exercising and stretching muscles to keep them healthy, the notion that the body works as a complex, dynamic structure designed to function naturally is less familiar to us.

			The basic premise of this book is that the musculoskeletal system—muscles, bones, and connective tissue—forms a complex structure that works dynamically to support us against gravity, and understanding how this structure works is the key to healthy musculoskeletal function.

			In this chapter—and in the pages that follow—I present a new and revolutionary model of how the body works based on practical and concrete knowledge of muscles, bones, and connective tissue and how they cooperate to form a complex, coordinated whole.

The Body in Action

			As a moving machine, the human body is one of evolution’s greatest marvels. Our ability to walk on two feet, to run, dance, climb, and throw, to make things with our hands, and to speak makes us the most skilled movers on the planet. Although many of these skills require learning, we acquire them—and are motivated to learn them—at a largely instinctive level. By the age of five or six, the typical child is capable of an enormous variety of skilled actions, refining and expanding on these skills for decades to come.

			 				When we are young, we learn actions with relative ease, and the musculoskeletal system—even when we have not fully mastered the use of it—seems to function effortlessly. Not so as we get older. By the time we are in our thirties, most of us cannot sit in a chair, or use our arms while sitting at a computer or playing an instrument, for more than a few minutes without discomfort. Increasing numbers of young people complain of back pain, and musculoskeletal conditions have become the leading cause of disability worldwide. Although we become more skilled with age, the quality of our actions tends not to improve but to deteriorate.

			But what accounts for the difference between the easy, poised grace of young children and the awkward, debilitated actions of many adults? Because we experience specific problems, we typically attribute the cause to the immediate problem—ruptured disc, strained muscles, injured shoulder—and treat it. Aren’t strain and discomfort an unavoidable consequence of work, stress, and life in general? Young children spend all their time at play; as teenagers, we are forced to sit in classrooms for hours on end. Life is stressful; as we age, we lose muscle mass, our tissues deteriorate, and we should not expect our bodies to function as well as they did in childhood.

			As we’ll see in this book, however, the reason children enjoy such natural functioning is not simply because they are young and healthy but because their musculoskeletal systems function naturally as a whole. We have only to look at how a child stands and sits to see that their system works as a coordinated whole. The body as a whole is supported naturally and easily, all the muscles are lithe and toned, and the various parts work together to produce effortless support against gravity. In the normal adult, these elements are missing because the elements that make up the whole are working improperly based on harmful patterns of action that, over time, interfere with this system.

			The notion that there is a natural movement system and that this system is the basis for healthful, efficient functioning is something that many of us intuitively understand. Yet how—or why—the body works in this way has never been fully articulated or understood. The different parts of our anatomy—shoulders, back, hips, and so on—make up a dynamic relationship of parts that, when organized properly, are designed to function easily and effortlessly. Making sense of how this system works as a coordinated whole is the subject of this book.

The Dynamic Role of Muscle

			It is tempting, when we speak about the musculoskeletal system, to look first and foremost at muscles. To perform a movement—to lift a glass, to walk down the street, or to type a letter—we have to contract, or tighten, particular muscles; otherwise we would not be able to move in space, manipulate objects, speak, or even breathe. The ability to move is organized by the nervous system, which sends signals to muscles that cause them to contract and other signals that tell muscles not to contract. At least, this is the usual view of what muscles do. What complicates the situation is that, in order to move in space or even to move an arm, we first have to keep ourselves upright in the field of gravity—in other words, we have to maintain postural support. Most of us have heard about the postural muscles that keep us upright—the deeper muscles of the neck, back and spine, and legs. By contracting, we are told, these muscles keep the head from toppling forward, the trunk from buckling, and the legs from collapsing under us.

			 				 				 					Fig. 1-1. When the head is allowed to balance naturally, the muscles of the spine can lengthen.

			But exactly how do postural muscles work? When you lift a heavy book, muscles in your shoulder and arm forcibly contract, moving the levers of the arm and maintaining the weight of the book. Using a great deal of force to accomplish the task is a perfectly acceptable strategy because you don’t have to hold the book up for very long. If your arm tires, you can soon put the book down and rest your muscles. Maintaining postural support of the body is a different matter. To support the entire body in the gravitational field, muscles have to maintain the support of the trunk for hours at a time, and trying to do this by simply contracting muscles would lead to exhaustion and dysfunction. How, then, do muscles and bones actually work together to support the body as a whole?

			 				The answer is that they don’t simply contract but work in a dynamic partnership with bone. The muscles on the nape of the neck, for instance, must maintain the support of the head, which would otherwise fall forward. But they don’t perform this function simply by contracting and pulling on the head, which would cause the head to be constantly pulled back and fixed in place. Instead, the head is weighted in front so that it exerts an opposing force on the neck muscles and keeps these muscles lengthened. The neck muscles can then pull on the head but, instead of forcibly pulling it back, they are stretched between the head and the spine so that, even while the muscles contract, the skeleton maintains length in the muscles (Fig. 1-1).

			 				 				 					Fig. 1-2. Muscles don’t simply act on the spine but are lengthened between attachments, forming a complex rigging for upright support.

			Another structure that exhibits this dual tendency is the spine. Muscles must pull on the spine but, if this was all they did, the spine could not maintain its lengthened support against gravity but would be dragged down by the muscles. Instead, muscles are lengthened between vertebral attachments and ribs and, in this context, maintain the support of the spine (Fig. 1-2). This arrangement explains how muscles act on bones as a basic way of supporting the skeleton. In order to produce force, muscles must contract—something we see every day in humans and other vertebrates. To maintain basic postural support, however, muscles must lengthen between the bony structures to which they attach so that, even as they act on bones, they are lengthened between bones—a subtle and dynamic arrangement in which muscles and bones work together to produce support against gravity. Some variation of this relationship exists in virtually every part of the musculoskeletal system. Instead of simply contracting, the muscles are suspended within a latticework of bones in such a way that, even while they maintain the stability of the skeleton, they are lengthened between the bony structures they support.

The Body’s Tensegrity Design

			If muscles don’t simply pull on bones but are lengthened between bones, how then can we explain posture and musculoskeletal support? According to the traditional biomechanical view, bones form a supporting framework upon which muscles act to maintain posture and to produce movement. In this model, muscles contract to support (and move) the bones, and length is not a key part of the equation. There are two cases in which muscles do in fact lengthen: when muscles are eccentrically contracting (as when you lower yourself by your arms), and when they are passively lengthened (as when you stretch your calf muscles). In the first case, the muscle is still actively contracting; in the second case, the muscle is being acted upon and is not performing a useful function. Muscles still perform only one function, which is to contract, or shorten.

			 				Here, however, we see something quite different. Muscles do not appear to actively contract at all but instead seem to lengthen between bony contacts, and yet they support body parts. How is it possible that muscles can lengthen rather than contract, and yet produce upright support? The answer is provided by the concept of tensegrity. In a tensegrity structure, no fixed supports hold things up, just guy wires and struts, yet these two elements, working together, are all that is needed to produce a self-supporting structure. In this model, muscles don’t act on bones but are embedded within a latticework of muscles and connective tissues. According to this quite different kind of model, upright support is achieved not by the bones, but by the larger network within which bones float.

			 				 				 					Fig. 1-3. A tent with a single pole and guy wires is supported through tensegrity principles.

			 				A simple example of a tensegrity structure is the old-fashioned tent (Fig. 1-3). This tent has no supporting walls, just the central pole. The pole holds up the walls of the tent but, at the same time, the walls of the tent support the pole. In this arrangement, opposing forces create support—the pole resisting the pull of the tent walls and the tent walls acting as tensile structures that resist stretch and keep the pole from falling. In more complex tensegrity structures, the poles, or struts, float within a network of guy wires, creating a supporting structure held up mainly by the guy wires and not the struts (Fig. 1-4). In this case, the struts float within the network of guy wires, providing no direct support, yet miraculously the structure seems to maintain support against gravity. In the human design, bones float within a network of connective tissue and muscles carry most of the load, creating a flexible, supportive structure that is both efficient and mobile.

			 				 				 					Fig. 1-4. Geodesic domes, such as the biosphere in Montreal, are tensegrity structures.

			 				Tensegrity structures are often compared to more traditional structures such as columns, arches and walls, which are designed to resist compression and to bear weight. Whether made of bricks, girders, blocks of stone, dried dirt, or concrete, compression structures have been used for centuries in the construction of cathedrals, coliseums, temples, aqueducts, and houses of all kinds. A tensegrity structure, in contrast, combines rigid compression members and tensile members to produce a strong, lightweight structure. The word tensegrity—a combination of tension and integrity—is a term coined by Buckminster Fuller, who developed the concept.1 In tensegrity structures, the rigid members don’t bear weight but provide opposition to the tension members, which in turn pull on the compression members. A tensegrity structure, then, can be defined as a continuous tensile network, interspersed with struts that create framing against which the tensile elements pull. In such a structure, much of the work is borne by the tensile members, which distribute the strain evenly throughout. This makes for a very efficient design that is lighter and stronger than walls or beams and uses less material.

			Because tensegrity structures are artificially engineered utilizing tensile wires and struts, they appear to be advanced and hi-tech. In comparison to those found in nature, however, such man-made structures are in fact rather crude. The tensegrity dome shown here utilizes regularly spaced struts and guy wires; in animals we find vastly more sophisticated structures, such as the rabbit pictured here (Fig. 1-5). In humans, this design reaches a pinnacle of complexity and subtlety that makes it possible for us to perform an amazingly diverse array of activities while distributing the workload over many meters of connective and muscle tissue; this way the burden does not fall on just a few muscles but is borne by all. Specific muscles perform work, but in the context of a larger, dynamic system in which bones are suspended between tensile structures, enabling the system as a whole to maintain support in the gravitational field with a minimum of effort and strain.

			 				 				 					Fig. 1-5. A line drawing of the musculoskeletal system of a rabbit reveals complex tensegrity elements.

			 				Since Buckminster Fuller popularized the concept, tensegrity has been widely studied and, in the newly applied field of biotensegrity, is being used to model living organisms.2 At the simplest level, it is now clear that muscles do not act as singular structures but are, in fact, part of a larger network of fascia and connective tissue. One key role of fascia is to distribute directional forces and to transmit these forces across bony boundaries.3 Good examples of this, which we’ll look at in detail in Chapter 6, are the spiral muscles that wrap around the trunk. Because the oblique muscles of the trunk are separated in front and back at the midline, forces are transmitted across the midline by means of fascial networks to form larger systems that wrap continuously around the body (Fig. 1-6).

			 				 				 					Fig. 1-6. Fascia combines with muscles to produce continuous lines of force, shown here in the trunk region.

			Until fairly recently, fascia was thought to be a rather inert structure, but it turns out that fascial tissue possesses its own tensegrity architecture, sometimes referred to as the extracellular matrix.4 This viscoelastic structure, like the larger tensegrity architecture of the body, resists deformation and, at the same time, distributes and responds to deformation over the entirety of its structure. At an even deeper level, the cells within the extracellular matrix are prestressed tensegrity structures that respond holistically to pressure.5 Thus the tensegrity design of the body at the macro level (connective tissue, muscle, and bone) is supported by tensegrity at the micro levels, constituting a nested, multifractal tensegrity design.

The Contractile Function of Muscle

			In our account of musculoskeletal function, muscles contract to produce movement, but they also work in a coordinated fashion to produce total bodily support in a gravitational field. Within this larger framework, muscles do not simply pull on bone but lengthen between their bony attachments and, in this context, maintain tone in order to create postural support. Therefore, to form a complete picture of how muscles actually work, we must describe two elements of muscle function: how they contract to perform work, and how they lengthen between bony contacts as part of their supporting function. The contractile function of muscle, which we’ll look at first, is well understood and, as we’ll see, is essential to understanding the second function.

			Muscle fibers are long, thread-like cells bundled together to form muscles, which are attached to bones to produce movement. In highly specialized organs, like the eye, muscle fibers are a fraction of an inch long, and only a very few are sufficient for the job at hand; in other parts of the body, such as the thigh, these fibers can be up to two feet long, and many thousands are bundled together to form powerful, bulky muscles that make it possible to walk, jump, and run on two feet (Fig. 1-7).

			 				Just as a muscle is made up of many individual muscle cells, or fibers, each muscle cell is made up of tiny, thread-like myofibrils, which are the contractile units within each muscle cell that make it possible for the muscle to perform work. Within each fibril are two types of molecular chains—the thin actin and the thick myosin chains—that are stacked together in such a way that the two types of filaments interdigitate, giving the muscle the banded or striated pattern after which striated muscle is named (Fig. 1-8).

				 				 				 				 					Fig. 1-7. The cross section of a typical muscle reveals bundles of individual muscle fibers, which themselves are composed of myofibrils.

			 				 				 					Fig. 1-8. a. A single myofibril showing an ordered patterning of myosin and actin strands; b. The interdigitation of the myosin and actin strands accounts for the muscle’s striated appearance.

			It is the ratcheting movement of the thin filaments in relation to the thick ones that produces contraction of the muscle, which is set off by chemical activity within the myofibrils. The myosin filaments have regularly protruding globular heads that are capable of binding at particular regions on the actin filaments. In a relaxed muscle, the myosin heads do not come into contact with these sites on the actin molecules because they are blocked by troponin molecules. In this state, the myofilaments are able to slide alongside each other, allowing the muscle to be passively lengthened. When the muscle fiber receives a signal from its motor nerve, however, this releases calcium ions into the myofibril space, which bind with the troponin molecules, changing their shape and exposing the binding sites along the actin molecules. The globular heads of the myosin molecules now bond at regular intervals along the actin molecules, forming cross-bridges between the actin and myosin strands (Fig. 1-9).

			 				 				 					Fig. 1-9. The globular heads on the myosin chains bond with the actin chains to form cross-bridges.

			One of two things can now happen. If the myosin heads remain bonded along the actin strands, the cross-bridges create stiffness or tone in the muscle because the interdigitating strands are now linked together and cannot slide alongside each other. The muscle then resists being lengthened—exactly what we see when a muscle is not entirely relaxed but maintains stiffness or tone, which maintains postural support.

			 				The second possibility, of course, is that the muscle can actively contract or shorten. In this case, the myosin heads only momentarily form cross-bridges because they continue to bond at adjacent sites along the actin chain, rotating and drawing the actin chain along the myosin chain (Fig. 1-10). This happens because, when the myosin head attaches to the actin filament, it pivots, or rotates, which moves the actin filament in relation to the myosin filament. After each rotation, the myosin head detaches, straightens itself out, reattaches at a new point on the actin chain and, through this continuous ratcheting action, draws the actin chain along the myosin chain. This telescoping of the actin and myosin strands, which can be seen on an electron microscope as a narrowing of the striations in the muscle, causes the muscle fiber as a whole to shorten, or contract. All of this is what we would describe as normal muscle function. Muscle contraction is produced at a molecular level when the motor nerve sets into motion the chemical changes that cause the interdigitating strands of myosin and actin molecules to slide over one another and thus shorten the muscle.

			 				 				 					Fig. 1-10. a. Chemical changes in the muscle allow the myosin heads to bond with the actin chain; b. The ratcheting action of the myosin heads along the actin filament causes it to move along the myosin chain toward the H zone.

The Second Function

			So much for the contractile component of muscle function; let’s look now at how muscles lengthen between their bony attachments. We’ve seen that, when a muscle contracts, the interdigitating strands of molecules within the myofibrils slide alongside each other to contract or shorten the muscle, shown here in schematic form (Fig. 1-11). In contrast, muscles that perform basic postural duties (such as those at the back of the neck) do not actively shorten but lengthen between their bony contacts. This, of course, is not something they “do” but, as we’ve seen, it happens naturally as part of how muscles work with bones to form a supportive structure.

			 				 				 					Fig. 1-11. a. At rest, the fibers in the muscle cell are lengthened; b. As the muscle fibers shorten through ratcheting action, the muscle contracts and acts on the bone to produce movement.

			 				But exactly what does it mean for muscles to lengthen, and how does this differ from muscle contraction? Consider what happens when we slump in a chair and the head is pulled back by shortened neck muscles. In this posture, the extensor muscles of the back are inactive and, because the spine lacks the support it needs to maintain its length, the trunk collapses into the slumped state. With the head pulled back in this way, natural upright support is virtually impossible because, instead of exerting an upward force on the neck muscles, the head is pressing down on the spine and the spine is unable to lengthen.

				 				 				 				 					Fig. 1-12. a. A heavy body part (such as the head) can be held by shortened or contracted muscles; b. When a muscle stops contracting, gravity intervenes and the part drops; the muscle is stretched and the actin and myosin strands slide apart.

			 				To restore postural support, we must stop pulling the head back so that it is not actively pressing down upon the spine and the trunk can come to its natural length. But restoring length is not simply a matter of making postural adjustments or stretching shortened muscles. In order to lengthen, the neck muscles must first stop contracting, which in turn allows the head to move upward, shown here again in a schematic way that corresponds to how a four-footed animal’s head is balanced at the end of its spine (Fig. 1-12). When this happens, the muscles are able to assume their natural length in the context of their bony attachments, triggering stretch reflexes that cause them to tone up and to resist being lengthened further (Fig. 1-13).

			 				 				 					Fig. 1-13. a. When gravity acts on the head, the head in turn pulls on the muscle, which becomes over-stretched; b. Stretch receptors in the muscle trigger tonic reflexes that counter the gravitational force; c. When the tonic reflexes are triggered, motor signals to the muscle enable it to resist further stretching.

			 				To address the practical problem of muscle tension, then, we have to understand how muscles that are contracting must release or let go so that they can lengthen between their bony attachments. For this to happen, the cross-bridging that takes place during contraction must cease so that the molecular strands are able to slide apart from each other. Understanding this dual function of muscles is an essential part of what it means for muscles to be healthy. Muscles that are chronically contracted must be able to stop contracting so that they can actively lengthen between their bony attachments. This is a dynamic state that exists only in muscles that are actively performing their functions within a dynamically supported, bony framework. When working in this way, muscles take on a healthy, spongy quality that can be felt to the touch—neither overworked, as in chronically shortened muscles, nor flaccid, as in muscles that have become weakened because they are no longer serving their tonic function. Producing this condition of muscle tissue is not simply a matter of releasing muscles by treating or stretching them; muscles lengthen in the context of a skeletal framework and, in this context, are designed to maintain natural length, as we see in this image of a young child (Fig. 1-14).

			 				 				 					Fig. 1-14. The natural poise of young children as they move their upper limbs to play is indicative of healthy lengthened muscles and tonic support.

Proprioception and Muscle Length

			To summarize what we’ve said so far, the body is not a simple bony framework acted upon by muscles but comprises a complex tensegrity system in which bones, connective tissue, and muscles cooperate to form a supporting structure. What has stood out in this model is the fact that, instead of pulling on bones in a crude manner, muscles actually lengthen between their bony attachments, creating an interactive structure that distributes forces throughout the system, and in such a way that the entire system works as a coordinated whole.

			 				For this system to work, however, it is not enough for muscles to be lengthened; in order to support the skeleton, they must also maintain tone or stiffness in response to the stretch exerted by the bony members of the skeleton. How do they do this? Part of the required force is produced by the nature of the tensegrity system itself. In the traditional view, muscles are motors that pull on bones, but in a tensegrity system, muscles pull inwardly against the outward pull of the struts, making the system pretressed.6 When the connective tissues are lengthened even further by adding greater load, the tensile structures store kinetic energy, which further increases the stiffness and resistance in the muscles—something that can be felt, in a healthy and naturally prestressed system, as liveliness and bounce.7 This ability of muscle tissue to firm up and gain efficiency in response to stretch appears to be built into the design of muscle tissue itself. Within their myofibrils, muscles contain strands of proteins known as titin; when lengthened, these molecular strands respond by firming up the muscle, adding force with no added metabolic demand being placed on the muscle.8 In short, the tensile component of muscle and connective tissue, acting within the context of the body’s tensegrity architecture, contributes significantly to the tone and strength of the system.

			Muscle tone is also maintained by higher centers in the brain. When I lift my arm, the movement is produced by the contraction of muscles that are activated by motor nerves. A nerve impulse, which begins at the higher cortical centers of the brain, carries a motor message to the muscles, which is combined with other nervous impulses to produce coordinated movement. But this isolated activity takes place in the context of a larger system of muscular support. If, for instance, I raise my arm, many muscles are involved in the support of the shoulder girdle and in the postural support of the body as a whole—a process that is far too complex to be directed piece by piece. We never just contract one muscle; the entire support system must constantly adjust itself in relation to whatever we are doing as the background against which specific contractions take place.

			 				This overall support, which produces what we all know as posture, is the work of stretch reflexes. In this context, we can no longer speak of muscles as discrete organs or as parts of a larger musculoskeletal system; muscles are part of a complex proprioceptive system designed to sense, and respond to, changes in this system. When our muscles become tight and sore, it is easy to become preoccupied with how tight they are and to assume, accordingly, that the solution is to release them or treat them. Virtually all myofascial systems—yoga, bodywork, massage therapy, and so on—address muscle tension in this way, as if muscles are unruly children that require our constant supervision. We forget that muscles are controlled by the nervous system in the most subtle and remarkable ways and that, furthermore, they are invested with sensory organs that constantly send feedback to the nervous system, comprising a system of remarkable subtlety and sophistication.

			 				This suggests that there is a great deal more to the problem of muscle tension than the fact that muscles become too tight and require stretching. And yet, for the most part, we have studied these functions—the motor nerves that tell muscles to contract and the muscle spindles that give information about muscles—as a sort of fixed system that simply does what it needs to do. If something goes wrong with our muscles, we assume they are simply shortened and require the aid of a massage therapist or yoga instructor; we have little to say about what has gone wrong (or even if it has gone wrong) and how the system can function more efficiently. When we understand the dynamic role of muscle tissue within the bony framework of the skeleton, however, we can begin to say something much more definite and meaningful about muscles and how to address muscle tension. When we restore length to muscles, they respond by toning up, at an entirely automatic level, in response to this length. If, for instance, shortened back muscles begin to lengthen, they now do less work and support the trunk more efficiently, paradoxically producing greater effect with less effort. Muscles all over the body function in this way as part of a larger system that maintains support with minimal work.

			 				 				 					Fig. 1-15. A tonic reflex is generated when a spindle in the muscle responds to stretch by sending a signal to a motor nerve serving the same muscle.

			 				But why should muscles that are letting go provide support? To put it another way, why should muscles contract more effectively when they are letting go? Shouldn’t letting go mean that, instead of providing more support, they provide less? The answer is that muscles are designed to respond to length—that is, they are wired in such a way that, when they lengthen, the muscle spindles, which are designed to sense stretch, send automatic signals to tell the muscle to contract at a low-level, constant rate—otherwise known as muscle tone (Fig. 1-15). What this means, in practical terms, is that muscles don’t need to lengthen simply because they become too tight and need to relax. They are meant to lengthen as part of how they perform their supporting function and, when they do, they tone up accordingly. Releasing a muscle by stroking or massaging may provide relief, but it cannot achieve real lengthening and in fact tends to override this system by desensitizing and over-stretching the muscle tissue. It is only when muscles actively lengthen as part of a dynamic system that the stretch reflexes are activated and the muscles tone up in response.

			Length is also the basis for heightened proprioceptive awareness. Trying to kinesthetically sense what is going on in our muscles as the basis for making direct changes may seem constructive, especially when we associate kinesthetic awareness with forms of release that relieve strain and tension. But awareness has little value if it cannot be applied in activity, and the only way to become aware in action is to establish natural muscle length based on the coordinated working of the system. When the body works as a dynamic whole, we awaken the kinesthetic sense in new ways, and can begin to sense how we interfere by shortening muscles. In this way, we can establish a meaningful foundation for becoming aware of what we are doing in activity. Establishing length in muscles thus serves as a crucial foundation for becoming proprioceptively aware in the context of a holistic dynamic system over which we can gain greater control.

			The sensitivity of stretch receptors to dynamic length in muscles tells us that the nervous system is not a static structure that regulates the musculoskeletal system but is, in turn, influenced by the working of this system. The nervous and musculoskeletal systems interact in a reciprocal relationship in which the nervous system regulates muscle tension, and proprioceptive function is in turn directly dependent on how the musculoskeletal system functions as a dynamic, working whole. Understanding this makes it possible to translate what we know about neural function into meaningful terms that, as we will see in this book, can be applied in a very practical way to muscles and sensory awareness.

The Central Role of the Head and Spine

			We have seen that, for the body to work as a total system, muscles must work in a dynamic partnership with bone to produce lengthened support. This is not only an efficient way for muscles to maintain the postural support of the skeleton, it is also how muscles register changes in length so that motor nerves, in turn, can maintain proper muscle tone. Muscles, working in conjunction with the skeletal framework, thus function as a central component of a neural and motor system of remarkable subtlety and complexity.

			 				But not all muscles are the same. When we lose postural support and go into a slump the head is pulled back and exerts downward pressure on the spine. To restore natural support, the neck muscles must lengthen so that the head can balance forward, removing the downward pressure and allowing the spine to lengthen. It is not a coincidence that we are focusing here on the head. Sitting atop the spine, the head is the highest point in the body, which means that, to maintain upright posture, the head must not be pulled down but move (for want of a better word) in an upward direction. In humans, the head leads the body as a whole, and the spine, in turn, has to lengthen to maintain the upward support of the body as a whole. In other words, the head and trunk form an essential foundation for movement.

			This central role of the head and trunk applies even to the use of the limbs. If, for instance, you reach with your arm to pick something up, you must engage specific muscles of the shoulder and upper limb. But the muscles of the shoulder and arm never work in isolation from the head and trunk, which must be supported and stabilized as the basis for using the arms. When we use the limbs, the muscles supporting the head and trunk form the essential foundation for the use of the limbs and are, in this sense, central to all other movement.

			Even when we are simply sitting and using our arms, the head/trunk relationship—and our tensegrity design as a whole—is fundamentally connected with movement in space. As vertebrates, we evolved from marine creatures that possessed a tubular gut with a mouth at the front end (Fig. 1-16). Muscles along the length of the body moved the fish in a forward direction, based on sensory input received at the front end (Fig. 1-17).

			 				 				 					Fig. 1-16. The precursors of vertebrates were marine animals that propelled themselves through the water by laterally flexing the body.

			 				 				 					Fig. 1-17. Fish possess a rigid spine which enables more efficient movement in a forward direction.

			This arrangement changed quite dramatically in fish that used their fins to move about in the shallows and then began to crawl onto land. In this case, the fins became functional levers for moving on the ground. To move on land required new kinds of support against gravity. In a marine environment, a fish is buoyed up by the water and therefore lives in a world that is virtually gravity-free. Animals on land, however, have to contend with the pull of gravity; to move efficiently in space, they must first raise themselves off the ground. Some reptiles accomplish this task with their bellies close to the ground and their legs splayed out to the sides; mammals walk and run with their legs more directly underneath them, making it possible to move quickly and efficiently on land. Here, the spine comes into play in a completely new way, functioning as a kind of bridge for supporting the body on the forelimbs at one end and the hind limbs at the other (Fig. 1-18). The musculoskeletal system of terrestrial animals thus serves a dual function: first, it produces overt movement by acting upon bones as levers; second, it counteracts the tendency of these levers to buckle so that, as the animal moves about, the body can be supported on its four limbs. The overt function of muscles in producing movement now takes places against the background of a prestressed, toned tensegrity structure maintained by muscle tone, organized around the head and trunk relationship, and moving directionally in space.

			 				 				 					Fig. 1-18. In mammals such as a cat (inset) the spine forms a bridge between the fore and hind limbs.

			In humans, this horizontal design has been modified for upright balance on two legs. This places the spine, as well as the muscles that support it, in a vertical arrangement. The system now lengthens upward against gravity and not in the direction of movement; but all action—even when it just involves sitting and using the arms—is still organized around the head and trunk, which lengthen upward as part of our upright design (Fig. 1-19).

			 			 				 				 					Fig. 1-19. In humans, the horizontal spine of a four-footed animal has evolved to a vertical position.

Dynamic Opposition and the Principle of Effortlessness in Nature

					The notion that muscles pull on bones to produce movement is a basic biomechanical concept going as far back as Leonardo da Vinci, whose drawings of bones and muscles as a kind of lever/pulley system (Fig. 1-20) provide an enlightened account of the natural mechanics of movement. Yet such a view cannot explain how action takes place in a living, breathing animal for two reasons. First, when muscles contract, this action pulls bones together, which creates fixation and loss of mobility of the parts in question. Although specific muscles can act on particular parts in this way without detriment to the whole, if all the muscles did this, the entire structure would lack flexibility and fluidity. In order for vertebrates to move efficiently, the entire skeletal framework must be fluid and mobile, and contractions would disturb this overall fluidity. Second, muscle contraction requires a great deal of energy, and a living organism with limited resources cannot handle such a high metabolic demand. To meet these two requirements, moving structures are built upon tensegrity principles that lower energy expenditure by allowing muscles to remain lengthened while, at the same time, enabling relevant muscles to contract without compromising the fluidity of the whole.

					 					 						 						 							Fig. 1-20. A Leonardo da Vinci drawing depicting the biomechanics of muscle and bone.

					 						In order to work in this dynamic way, major segments of the body do not move toward each other but apart. When we forcibly contract a muscle, one part of the body is pulled toward the other; in the context of the body’s larger tensegrity architecture, body parts move in opposition. This creates a dynamic polarity that operates as a basic principle in vertebrate design, as we can see in the cat pictured in Fig. 1-21. Particular muscles are forcibly contracting, yet the neck muscles, instead of shortening, are lengthening in such a way that the head goes away from the spine and the spine lengthens as a whole. The same thing happens in humans except in a vertical orientation: the extensor muscles of the neck and back are active but, instead of shortening the spine and pulling the head toward the spine, the neck muscles lengthen so that the head goes up and away from the spine and the spine lengthens (Fig. 1-22). In other words, muscles don’t simply pull on bones; connectives tissues and muscles interact dynamically with bones to produce a supporting structure that is fluid and mobile. This is a basic principle in vertebrate movement in which a polarity of forces creates directional support in space with a minimum of fixation and effort. It is nature’s solution to the problem of vigorous and efficient movement, a kind of yin/yang of bodily motion and support.

					 						 						 							Fig. 1-21. In this frame-by-frame image of a leaping cat, we can see that the entire body lengthens as the cat prepares to jump.

					 						 						 							Fig. 1-22. In effortless, efficient sitting, the head balances naturally on the spine and the muscles of the neck and back lengthen.

					Once we understand how this system works, we can see that forms of movement or treatment that address muscular tension in purely structural terms cannot establish the dynamic conditions required for efficient animal movement. Structure is important, but no amount of structural work can establish these dynamic relations, which depend upon the dynamic working of the system as an energized, living whole. The same can be said of exercise, which works on the misguided assumption that the main function of muscles is simply to pull on bones and completely leaves out the dynamic quality of muscle function. Both approaches are unidirectional, mechanical concepts, and nature does not work on the unidirectional or mechanical principle; it works on the principle of dynamic opposition and polarity of forces. Compression presses outward and muscles pull inward. The combined action creates direction of parts with a minimum of effort—a principle we see everywhere in nature, exhibited as litheness and effortlessness in action (Fig. 1-23).

					 					 						 						 							Fig. 1-23. The effortless stretching and twisting of this agile cat is indicative of litheness in movement as a principle in nature.

					The same principle applies to the concept of relaxing muscles to reduce tension. Because so many of us suffer from excess muscular tension, it is easy to think that release of tension is the main quality we’re looking for in muscles. But muscles do not need simply to let go or release; they must let go in the context of a skeletal framework in which parts move in opposition, producing the dynamic complementarity required for mobile yet forceful movement. Achieving this quality is not just about muscle release but about directional energy. When, for instance, the neck and back muscles stop tightening in the context of dynamic length, the head moves quite forcefully in an upward direction, which it needs to do if it is to counteract the force of gravity and the falling weight of the body. When this happens, the head actually pulls in an upward direction, producing energetic support and directional movement based on the two-way polarity of tension and stretch. In cats, as we just saw, this lengthening takes place in the same direction as its movement in space; in humans, the oppositional lengthening force is upward because, although we move forward in space when we walk, we are oriented vertically and lengthen upward against gravity.

The Spine and Its Tensegrity Design

					 						A fascinating example of the concept of tensegrity support was reported some years ago in the New York Times. It compared European men carrying heavy loads on their backs to Kenyan women carrying weight on their heads (Fig. 1-24).9 The women, it turns out, carried 20 percent of their body weight with no additional expenditure of calories as compared to the men, who used far more effort. The study concluded that this was because the women altered their gait but did not alter their upright support mechanism when carrying a load on their heads, whereas the European men did and therefore had to use far more muscular effort to support the packs on their backs. In essence, each woman was able to carry the weight on top of her head by utilizing—and not disturbing—the tensegrity support of the musculoskeletal system, so that the load was distributed over the entire tensegrity structure rather than straining particular muscles.

					 						 						 							Fig. 1-24. Women carrying weight on their heads with a minimum of work.

					 						It has been long accepted that to support weight, the spine, which acts as a compression structure, must be acted upon by muscles that were viewed as the main agents in upright posture. It is now clear that as a supporting column, the spine is incapable of supporting heavy loads and that muscles can account for only a fraction of the force required to support heavy loads. What has been left out of the traditional equation is the role of fascia, which transmits and distributes forces throughout the skeletal framework.10 This new model suggests that the spine is not simply a compression structure but a complex tensegrity system in which fascia not only transmits forces but actively contributes to the support and stabilization of the spine (Fig. 1-25 and Fig. 1-26). This tensegrity model explains why it is possible to carry heavy loads on our heads without damaging the vertebrae and without straining muscles: bones are embedded within a fascial network that not only transmits and distributes forces but also relieves muscles of work.

						 						 						 						 							Fig. 1-25. When key muscles of the spine are depicted as lines, a complex tensegrity structure emerges.

					 						 						 							Fig. 1-26. The tensegrity patterning grows in complexity as more muscles are added, forming an elaborate system of rigging.


How the System Works

			It is a basic premise of this book that the musculoskeletal system is designed to work naturally and effortlessly, if only we take the time to understand this design and how it works. When something goes wrong with our muscles, we typically identify the specific symptom—a tight or strained muscle, inflammation, repetitive strain injury—and treat it with massage, strengthening, or stretching exercises. But the system works as a coordinated whole, and when we misuse a part, we misuse it as part of this whole. Treatment can be useful, but if we want to restore the natural and healthful function of the musculoskeletal system, we must understand how this system is designed to work and how muscles function in the context of this larger system.

			The idea that, when something is wrong, we should work on muscle and connective tissue that has become in some way distorted reflects the more general attitude that the body is supposed to work properly; if it doesn’t, we presume that something specific has gone wrong and it’s the job of an expert—doctor, chiropractor, physical therapist—to correct it, like a car that breaks down and gets brought to the mechanic. But the body is a complex, finely tuned instrument and, if you are experiencing constant backache or muscle strain, it means that you have been doing something to interfere with this system over time. To sit comfortably, for instance, the muscles of the back must be able to support the trunk, the spine must be naturally lengthened, and the hips must be free and released. When we habitually slump, all these systems become interfered with, and no amount of stretching or strengthening will correct these imbalances if we don’t understand how these systems are designed to work as a dynamic whole.

			As we will see in the chapters that follow, ten key systems contribute to the working of the musculoskeletal system; we will look at each of these systems, examining how the system in question is designed to work, what goes wrong with it, and how it functions properly. In addition, we will look at some basic ways we can encourage the proper working of each system.

			With this in mind, and before we look at the individual systems, it is useful to list a few of the key principles that govern the working of these systems.

1. Each system has a functional design.

			When we suffer from particular musculoskeletal difficulties, we are usually so preoccupied with addressing specific muscles or joints that we are unlikely to consider how the parts in question are designed to work. When, for instance, you are sitting for long periods and your back hurts, how are you using your back? Are you trying to sit up and, if so, are you overworking your lower back? The truth is that, if your back hurts, there is probably a good reason, and the solution is not to stretch or strengthen muscles but to understand how the back is designed to function in its supportive role. Every system has a key organizing principle; in each case, we identify the muscles that make up the system and the essential principle that governs its proper working.

How the Systems Work

					Here are some of the systems we will look at in this book in Chapters 3, 4, 8, and 9.

The Extensors of the Back

					The back muscles can be flaccid or shortened, but it does not follow that by strengthening or stretching particular muscles, the problem will be corrected. The proper function of the back depends on the length of the back muscles in relation to head balance (Fig. 2-1).

					 						 						 							Fig. 2-1. The lengthening support of the back.

The Flexor Muscles

					The flexor musculature is a tensile structure designed to support the ribs and abdomen and is suspended between points above and below (Fig. 2-2 and Fig. 2-3).

					 						 						 							Fig. 2-2. Loss of front length.

					 						 						 							Fig. 2-3. Restored front length.

The Shoulder Girdle

					The shoulders can be raised, narrowed, collapsed, and fixed; to work properly, the muscles of the shoulder must be toned and lengthened so that the shoulders widen apart (Fig. 2-4).

					 						 						 							Fig. 2-4. The widened shoulder girdle.

The Throat and Its Suspensory Musculature

					It is clear when there is a harmful degree of tension in the throat or when the tongue is harmfully depressed, as we can see in the photo (Fig. 2-5). But this does not tell us in a positive way how the throat is meant to function. To answer this question, we must understand how the throat is suspended from the skull and is thus maintained within a network of muscles that antagonistically support it (Fig. 2-6).

					 						 						 							Fig. 2-5. Depressed larynx.

					 						 						 							Fig. 2-6. Suspensory muscles of the throat

2. Length is a key principle of muscle function.

			Muscles are designed to contract, but they are also part of a larger tensegrity structure designed to produce support and movement. In this context, muscles are meant not only to contract but also to lengthen between their skeletal attachments, which is part of how the body maintains natural and effortless support (Fig. 2-7). The capacity of muscles to lengthen between their bony attachments is thus a fundamental property of healthy muscle tissue and the foundation for efficient support and movement.

			 				 				 					Fig. 2-7. Natural sitting posture with muscles lengthened instead of shortened.

3. Muscle groups function in the context of upright support.

			Although muscles in general are designed to contract to produce movement, specific muscles never function in isolation but are always part of a larger functional group, as in the case of arm movements, which involve torquing and spiraling the body. Even when we come to understand that individual muscles are part of functional systems, however, it is important to recognize that functional systems are themselves part of an even larger functional system designed to support us against gravity. Nowhere is this more true than with the spiral muscles, which are designed not simply to torque or twist the body but to maintain lengthened support against gravity, as we can readily see when we come out of a postural twist and the body releases into length (Fig. 2-8). What this means, in practical terms, is that muscles cannot be understood—or treated—individually or in functional groups but only in the context of upright support, which is the true basis for restoring normal function in muscles.

			 				 				 				 					Fig. 2-8. The spiral muscles are part of our antigravity support system.

Functional Muscle Groups Are Part of Our Dynamic Upright Design

					The spiral muscles of the trunk are designed to produce torsional movements of the body and, in this sense, have a clear functional purpose (Fig. 2-9). But this is not their only function. We have only to look at how these muscles attach to the skull to see that they are part of our upright design. For these muscles to function properly, they must lengthen in the context of the upright support system, as we will see in Chapters 5 and 6.

					 						 						 							Fig. 2-9. Spiral muscles make rotational movements possible.

4. The relationship of the head to the trunk is the key organizing principle.

			Although muscles contract to produce specific movements, such as flexing an arm or turning the head, movement in general is organized around the central relationship of the head and trunk. In four-footed animals, the head and spine are oriented horizontally to produce forward movement in space (Fig. 2-10); in humans, we are oriented vertically to maintain support on two feet, and all movement—whether forward locomotion in space or the fine motor use of the hands while sitting—is based on this upright support system, organized around the dynamic relationship of the head to the spine (Fig. 2-11).

			 				 				 					Fig. 2-10. Dog with head leading and body following in the direction of movement.

			 				 				 				 					Fig. 2-11. Human with head and trunk in vertical arrangement.

5. The key to the part is the whole.

			When we suffer from a specific problem, such as a painful shoulder, we normally identify the pain itself as being the problem or, if we attempt to make a more in-depth diagnosis, the inflammation or muscle strain that is causing the pain. This type of explanation may suffice in cases in which a specific problem requires treatment. When it comes to tension-related problems, however, this type of explanation tells us almost nothing, since it amounts simply to a description of the symptom, not an explanation of its cause. For instance, the working of the shoulder is entirely dependent on the working of the trunk, and shoulder problems are almost always part of a larger pattern of interference in the trunk. To address the shoulder, then, it is necessary not just to treat the specific symptom, but to restore the working of the larger system upon which the shoulder depends. In short, the whole is the key to the part, and a real understanding of how the different parts of the body work must be based on a practical understanding of this larger system.

6. The parts influence the whole.

			As a system of levers, the hand and arm are dependent on the whole but not essential to it—or at least, that is how the arm, as a biomechanical system, seems to work. But each system in the body—arms included—is not only dependent on the whole but can also influence it in profound ways. If, for instance, the shoulders are narrowed and the arms are heavy and collapsed, the torso is adversely affected, not to mention breathing, muscle tone, and overall upright support. To address the body as a whole, it is necessary to restore the working of the shoulder and arm, which, in turn, restores the working of the upright system. This is why we cannot look at the musculoskeletal system as a whole unless we understand how the parts relate to the whole and how the whole is affected by the parts.

7. Many systems, one response.

			Although we will examine individual systems in depth, it is important to remember that each one is part of a larger whole and contributes to the working of the whole. When working properly, these systems combine to produce effortless, expansive support of the body against gravity. Muscles lengthen between their bony contacts, the body is lightly and easily supported against gravity, and movements take place effortlessly and without strain in any part. This expansive movement, which involves the coordinated working of muscles all over the body, is the background against which all movement happens—the basic organizing principle of movement and the key to the musculoskeletal system (Fig. 2-12).

			 				 				 					Fig. 2-12. Child with a naturally functioning upright support system.

How the Chapters Are Organized

			Each chapter begins with a general description of the specific system being examined, how it is organized to work properly, and what goes wrong with the system, or what I somewhat playfully call contraindications. This overview is followed by black-and-white line drawings depicting the key muscles within the system, accompanied by a list of the origins and insertions of each muscle. We then examine the system in more detail, accompanied by numerous sidebars that explore specific aspects of the system. In examining each of these systems, the goal is not to list muscles and joints in exhaustive detail but to describe how the muscles work as functional systems. For a more detailed examination of musculoskeletal anatomy, see my earlier book, Anatomy of the Moving Body.1


Extensors and Head Balance

			The primary muscles that support us against gravity are the extensors of the back and legs. If you are standing and allow your body to go limp, you’ll notice that as you begin to fall, your head, trunk, and knees buckle forward. In order to prevent this buckling, the extensor muscles, which lie primarily along the back of the body, counteract this tendency by extending the legs and trunk. Because extension at the knee is performed by the quadriceps muscles on the front of the thigh, the extensors of the leg are on the front of the leg as well as in back.

The Lengthening Back

			When the muscles of the back are lengthened, the back maintains the support of the trunk with minimal effort. Acting as a counterbalance that opposes the pull of the extensors of the neck, the forward balance of the head on the spine is an essential component in maintaining stretch on this extensor sheet, enabling the muscles to provide support against gravity with a minimum of effort. In this context, the extensor sheet lengthens from the sacrum right up to the occiput, acting as a whole to maintain the support of the head and trunk.


Because we constantly pull the head back and shorten in stature when performing simple actions, the muscles of the neck and back become shortened. When coupled with the tendency to slump while sitting, which further disengages the extensor system, the back becomes harmfully narrowed and overworked in some places and flaccid in others. 			When we shorten in stature

			 				The neck muscles become shortened and the head is pulled back.

				The back is narrowed.

				The lower back muscles are shortened and contracted.

				The chest is raised.

			When we lengthen in stature

			 				The neck muscles release and lengthen.

				The head balances forward and up on the atlas.

				The back lengthens and widens.

				The back muscles become toned.

				The trunk lengthens.

			 				 				 				 					For vertebra and rib numbers listed in the table on the opposite page, see diagrams on pages 88 and 141.

			 				 					 						 Origin 						 Muscle 						 Insertion

				 				 					 						 Transverse process of atlas 						 1. Rectus capitis anterior 						 Occiput

					 						 Transverse process of atlas 						 2. Rectus capitis lateralis 						 Occiput

					 						 Spinous process of axis 						 3. Rectus capitis posterior major 						 Occiput

					 						 Atlas 						 4. Rectus capitis posterior minor 						 Occiput

					 						 Spinous process of axis 						 5. Obliquus capitis inferior 						 Atlas, transverse process

					 						 Transverse process of atlas 						 6. Obliquus capitis superior 						 Occiput

					 						 Sacrum/iliac crest 						 7. Iliocostalis lumborum 						 Ribs 7–12

					 						 Ribs 7–12 						 8. Iliocostalis thoracis 						 Ribs 1–6, C7

					 						 Ribs 3–6 						 9. Iliocostalis cervicis 						 Transverse processes C4–6

					 						 Iliac crest, sacrum, L1–5 						 10. Longissimus thoracis 						 T1–12, Ribs 4–12

					 						 Transverse processes T1–5 						 11. Longissimus cervicis 						 Transverse processes C2–6

					 						 T1–5, C5–7 						 12. Longissimus capitis 						 Mastoid process

					 						 Spinous processes T11–L2 						 13. Spinalis thoracis 						 Spinous processes T4–8

					 						 Nuchal ligament, C7 						 14. Spinalis cervicis 						 C2

					 						 Transverse processes T6–10 						 Semispinalis thoracis 						 Spinous processes C6–T4

					 						 Transverse processes T1–5 						 Semispinalis cervicis 						 Spinous processes C2–5

					 						 C5–8, T1–6 						 Semispinalis capitis 						 Occiput

					 						 Nuchal ligament/T3–T6 						 Splenius cervicis 						 C1–C3

					 						 C7–T3 						 Splenius capitis 						 Mastoid process/occiput

					 						 Ilium/sacrum 						 15. Gluteus maximus 						 Iliotibial (IT) band/shaft of femur

					 						 Ischium 						 16. Biceps femoris 						 Head of fibula

					 						 Upper shaft of femur 						 Quadriceps 						 Tibial tuberosities

					 						 Ischium 						 17. Semitendinosus 						 Below medial epicondyle of tibia

					 						 Ischium 						 18. Semimembranosus 						 Medial epicondyle of tibia

					 						 Condyles of femur 						 19. Gastrocnemius 						 Calcaneus

The Extensors

			Upright posture is a complex process maintained by the action of muscles that extend the head, neck, trunk, and legs. These extensor muscles are located largely on the nape of the neck, the back, the buttocks, and the back of the legs; the only exception is the quadriceps muscles that extend the leg at the knee, which are located on the front of the thigh (Fig. 3-1).

			 				 				 					Fig. 3-1. Extensor muscles of back, thigh, and calf regions.

			Two key groups of back muscles maintain erect posture. The first group is composed of a series of small muscles running in between the vertebrae of the spine along its entire length, from the sacrum to the occiput of the head. Attaching to the spinous and transverse processes of the vertebrae, these deep muscles act upon the vertebrae, maintaining the internal length and support of the spine (Fig. 3-2).

			The second group is the sacrospinalis or erector spinae muscles. In Chapter 5 we look in detail at the deep postural muscles of the spine that comprise the first group, but let’s look now at the second group, the sacrospinalis muscles. These are the long muscles that run lengthwise up and down the back, from the sacrum right up to the base of the skull in overlapping bundles that leapfrog from the bottom to the top, forming a continuous sheet of muscles supporting the entire back. When we are standing, lifting weight, bending down, or inclining forward, these muscles maintain the support of the trunk and thus play an essential role in our upright posture (Fig. 3-3).

			 				 				 					Fig. 3-2. Small postural muscles of the spine.

			 				 				 					Fig. 3-3. Sacrospinalis or erector spinae muscles.

			Toward the neck, these deeper layers are replaced by more superficial muscles: the semispinalis and splenius muscles. The semispinalis capitis muscle originates at the upper thoracic and cervical vertebra and, passing upward at an oblique angle, attaches to the occiput (Fig. 3-4). The splenius muscle arises from the seventh cervical vertebra and nuchal ligament and passes upward and outward to attach to the mastoid process of the temporal bone and the occiput (Fig. 3-5).

			 				 				 					Fig. 3-4. Semispinalis muscles.

			 				 				 					Fig. 3-5. Splenius muscles.

			At the most obvious level, the purpose of the muscles of the neck is to support and move the head. As part of the extensor system on the back of the body, these muscles play a central postural function—a function that becomes even more pronounced during the performance of strenuous activities that require the forceful action of the extensors to support and stabilize the neck and head.

Dynamic Muscle Length and Head and Spine

			To support upright posture, the extensor muscles of the spine maintain the support of the trunk and thus play a central role in upright posture. But although these muscles have work to do, they discharge their duty based on the central principle of muscle function described earlier: they must be in a lengthened state and maintain tone in the context of length. Looking at the extensor muscles and where they attach to the skull, you might think that, given how powerful they are, they should pull the head back. In a well-coordinated person, however, this is not what happens. Instead, the head seems to go upward and the muscles of the neck lengthen between their bony attachments (Fig. 3-6). There are two principal reasons for this. The first is that, although the head sits on top of a vertical-placed spine, most of its weight is forward of the point of balance so that it naturally falls forward. Because of this, the muscles of the neck don’t simply pull the head back but are kept stretched by the action of the head which, by falling forward, keeps the muscles from shortening. In this way, the muscles are maintained at their optimal length and, most of the time, perform their job of maintaining the balance of the head and spine without actively contracting.

			 				 				 					Fig. 3-6. The skull naturally falls forward, creating a dynamic equilibrium in which the muscles of the back are lengthened while maintaining the head in an upright position.

			The second reason is that the spine itself, acted upon and supported by a network of muscles and connective tissue, lengthens against gravity, which in turn helps to maintain the length of the long muscles of the back. Because the back muscles lengthen within this bony framework, the entire back feels full and supported, and we can maintain upright posture with a minimum of work and effort. This produces an overall lengthening response of the spine in which the head can be described as going up and the back as lengthening—that is, the head is not pulling back and down but balances forward so that the entire trunk, with the head leading on top, lengthens upward (Fig. 3-7).1

			 				 				 					Fig. 3-7. Even while using their hands, young children are able to maintain natural upright support with their head balanced forward and their spine lengthening.

			 				In many of us, however, this sheet of muscles becomes shortened and constricted so that, instead of supporting the trunk with lightness and ease, we are in distress much of the time, overworking these muscles and struggling even just to sit. To function properly, this entire sheet of muscles must lengthen in such a way that the head, coming out of the back, exerts an upward pull upon this sheet so that the muscles, from sacrum to skull, can lengthen and the back can work in a full and supportive way. When we habitually slump, these muscles are disengaged, and the only way to sit upright is to arch the back. This strains the muscles of the lower back, as we quickly learn when we force ourselves to sit upright for a long time and the muscles in the lower back become fatigued and start to burn. This is not how these muscles are meant to work. When the head is balanced forward and the trunk comes to its natural length, the sacrospinalis muscles lengthen between their bony attachments and thus maintain tone in the context of length. In this way, this muscle group functions as a whole to maintain postural support without being strained in any particular region (Fig. 3-8).

			 				 				 					Fig. 3-8. When the postural system is working correctly (as in Fig. 3-7), the balance of the head, together with the lengthening action of the spine, creates effortless support against gravity.

The Universal Joint

					 						As the uppermost segment of the vertically poised body, the head sits atop the spine and, at this point, can both nod and rotate. Two joints make these movements possible. First, the skull sits on, and articulates with, the first vertebra of the spine—also known as the atlas because it holds up the globe of the skull—to form the atlanto-occipital joint. Two rounded bumps on the base of the skull, the occipital condyles, fit nicely into two concave depressions on the atlas, making it possible to nod the head up and down (Fig. 3-9).

					 						Second, the atlas, with the skull sitting on top of it, rotates around the second vertebra—called the axis because it forms the pivot, or axis, upon which the first vertebra rotates (Fig. 3-10)—to form the atlanto-axial joint. At the front of the axis is an upward projection called the odontoid process (meaning “tooth”), which extends up within the anterior arch of the atlas; the atlas, with the head sitting on it, rotates around the odontoid process, making it possible to rotate the head in relation to the spine.

					 						 						 							Fig. 3-9. The skull rocks back and forth on the atlas.

					 					 						 						 							Fig. 3-10. The atlas, with the head sitting on top, rotates around the odontoid process of the axis.

					So the skull can nod on the atlas, and it can rotate in relation to the spine because the first vertebra, with the skull sitting on top of it, can pivot on the axis. Together these articulations form a “universal joint” that makes it possible to both swivel and hinge the head (Fig. 3-11).

					 						 						 							Fig. 3-11. Movement of the head at the atlas and axis makes a universal joint, allowing the head to nod and turn.

Head Balance

					As a spherical object, the head seems to be balanced rather evenly on top of the spine. In fact, the skull is elliptical or egg-shaped and sits on the atlas at a point that is well behind the center of gravity. This means that more of its weight is in front than in back, which causes it to nod or fall forward (Fig. 3-12). Add to this the mass and weight of the jaw, and it becomes clear that the skull is unevenly balanced on the atlas so that its natural tendency is to nod forward at the atlanto-occipital joint (Fig. 3-13).

					 						 						 							Fig. 3-12. Model of head balance in humans.

					 						 						 							Fig. 3-13. The skull (along with the jaw) is weighted forward on the atlas.

The Animal Origins of Our Upright Design

					 						Although the human upright posture is a unique design found nowhere else in the animal kingdom, it is nevertheless a modified version of the posture of the four-footed animals from which we evolved. In a cat or horse, the head hinges at the front end of the horizontally oriented spine and, in this cantilevered position, exerts stretch on the neck muscles, which in turn maintain the posture of the head (Fig. 3-14). Although radically altered in humans, something of this four-footed arrangement is preserved in the upright human posture, where the head, sitting on top of the spine, sits off balance, and thus continues to exert stretch on the neck muscles. In contrast to the horizontal pull of the cantilevered skull in the four-footed animal, however, the forward balance of the skull on the vertically positioned human spine acts upward against the downward pull of the muscles (Fig. 3-15). This is a very different arrangement than in the four-footed animal. There, the cantilevered head produces a very powerful horizontal pull on the neck muscles which, in turn, maintain tone in the neck to support the weight of the head. In the upright human design, the muscles of the neck and spine pull directly downward, and the forward tilt of the head acts upward on the back of the skull to counteract the downward pulls. This arrangement is more easily disturbed than that of the quadruped because, unlike the animal’s head, the human head can easily be pulled backward, thus disrupting the upright support system (Fig. 3-16)—a fact that at least partially explains why humans are so prone to slumping. To counter these downward forces, the head must retain its off-balance position on the spine. The forward balance of the head in relation to the spine is thus an essential feature of the upright human postural system.

					 						 						 							Fig. 3-14. Head balance in a cat.

					 						 						 							Fig. 3-15. Human head balance.

					 						 						 							Fig. 3-16. Pulling the head back disturbs its natural forward balance on the spine and interferes with upright posture.

The Plumb Line

					We are all familiar with anatomy charts that depict upright posture as a series of parts stacked vertically on the plumb line (Fig. 3-17). This would suggest that, to maintain upright posture, the extensors in back and the flexors in front balance each other to keep us from falling over. But this is not how we are actually designed. We evolved from four-footed animals that, to come upright, had to raise the trunk at the hips. This places the bulk of the demand on the extensors of the back, which have to maintain the support of the trunk. Even when we are standing fully erect, the trunk wants to buckle forward; if we incline forward, bend down, or lift weight, the trunk needs even more support in back (Fig. 3-18). It is the sacrospinalis muscles—as well as the other extensors of the neck, hips, and legs—that bear the brunt of this labor and thus play an essential role in our upright posture.

					 						 						 							Fig. 3-17. Posture and the plumb line.

					 						 						 							Fig. 3-18. When the body is inclined, the action of the extensor muscles, and not the stacking of body parts, supports it against gravity.


Semi-Supine Position

					To restore length in the extensor muscles of the neck and back, try lying down in the semi-supine position with one or more books supporting your head so that it does not tip backwards, and your knees pointing to the ceiling (Fig. 3-19). It is important, when starting this exercise, to begin by doing nothing at all; this gives muscles that are holding a chance to let go. Then without actively moving, think about your head and knees going away from each other. This will allow your back to lengthen and fill out on the floor. As the muscles of the neck, ribs, and back begin to let go, you will feel that your trunk can begin to regain its natural length, your back can begin to lengthen and fill out on the floor, and your head can begin to come out of the back—a process that will happen automatically as muscles release and naturally tone up.

					 						 						 							Fig. 3-19. The semi-supine position. By simply thinking of the head and knees going away from each other, the muscles of the back are encouraged to let go into length.

					When this toning up happens, the back muscles lengthen and widen, producing the elastic and toned condition of the back that enables it to support the trunk efficiently and effortlessly when you are sitting and standing. This condition cannot be brought about by stretching and working on individual muscles or by positioning the head but instead is a natural condition of the muscles in which they are releasing between their bony contacts so that the