The Organization of Movement Four Talks on the …...muscle through the peripheral nerves or originate higher up in the brain and travel down to these peripheral nerves. In any The

16 www.AmSATonline.org AmSAT Journal / Fall 2013 / Issue No. 4

The Organization of Movement

In Part 1 (AmSAT Journal #3,

Spring 2013) we saw that muscles

form a complex webbed system that,

working in conjunction with the

latticework of bones, produces a

network of support based on an

architectural structure of elastic

stretch. This background system is

crucial to how we move; no specific

movement can take place without

this larger network of support.

For the system to work,

however, it is not enough for

muscles to be elastic, important

though this may be. They must also maintain tone in response

to the stretch exerted by the bony members of the skeleton in

order to support the skeleton and also to shorten to produce

movement. How do they do this? If I lift my arm, the

movement is produced by the contraction of muscles that are

operated by motor nerves. A nerve impulse beginning in the

higher cortical centers of the brain carries a motor message to

the muscles that combines with other nervous impulses to

produce coordinated movement.

But movement is more complicated than that. We saw in

Part 1 that specific movement takes place in the context of a

larger system of muscular support. For instance, if I simply

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. This process 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 the specific

contraction takes place. This overall support, which produces

what we all know as posture, is the work of stretch reflexes.

Muscle Sensors and the Stretch Reflex

The stretch reflex is the automatic contraction of a muscle

in response to being stretched. The most familiar example of a

stretch reflex is the knee-jerk test: the doctor uses a rubber

mallet to tap the patellar tendon just below the kneecap,

stretching the quadriceps muscle, which contains sensors that

register the change in length due to the stretch. These sensors

send an impulse to the spinal cord reporting the change in

length, which in turn excites the motor nerve innervating the

quadriceps and causes the muscle to contract, eliciting the knee-

jerk response (Fig. 1).

In this example, the doctor artificially produces a stretch

reflex for the purpose of testing muscles and reflex responses,

but the real function of the stretch reflex is to maintain stability

of body parts. When you are standing, gravity is acting on your

body and causing many of your joints to buckle, including the

knees. This buckling of the knees causes the quadriceps muscle

to stretch––just as the doctor’s mallet did. The muscle,

registering this change, sends an impulse back to the spinal

cord, which in turn sends an impulse to the muscle telling it to

contract. This contraction of the quadriceps keeps the knee

from buckling, thus maintaining stability in the leg. In its

simplest form, then, the stretch reflex is a basic reflex arc

designed to respond to stretch—not just in the knees but

throughout the body—so that parts of the body that are

buckling can be stabilized, thus maintaining posture. In this

way, the body’s elegant elastic system maintains constant

support and tone.

Fig. 1. The knee-tendon reflex

There is a great deal more to say about this process, but

first I want to address the basic nature of a reflex arc. Figure 1

shows the knee-tendon reflex. The quadriceps muscle on the

thigh is charged with the task of keeping the leg straight at the

knee. When the knee buckles, the quadriceps is stretched and,

in order to maintain the support of the leg, contracts in

response. Why should it be necessary for a nerve in the muscle

to send a sensory signal to the spine, and for another nerve in

the spine to receive this impulse and send a motor signal back

to the muscle, when the muscle could just respond directly and

avoid all that unnecessary and apparently redundant signaling?

To understand this, we must remember that muscles are

served by motor nerves with cell bodies located in the spinal

cord and axons that project out from the spinal cord as

peripheral nerves to the muscles. Signals for muscles to

contract originate either in the spinal cord and travel to the

muscle through the peripheral nerves or originate higher up in

the brain and travel down to these peripheral nerves. In any

The Organization of Movement Four Talks on the Primary Control

Part 2: Stretch Reflexes and the Musculoskeletal Framework: How Stretch Reflexes Convert the Musculoskeletal System

into a Spring-like Framework by Theodore Dimon

Theodore Dimon

AmSAT Journal / Fall 2013 / Issue No. 4 www.AmSATonline.org 17


case, the muscle receives the impulse to contract from a motor

nerve located in the central nervous system. The muscle does

not know when and how much to contract; that information can

only come from sensors in the muscle that register stretch in the

muscle. So the spinal cord must first receive an impulse from

the muscle sensor telling it when contraction is required, and

then send the motor signal to the muscle (Fig. 2) telling it how

much to contract.

Fig. 2. The reflex arc

Sherrington and the Study of Posture

C.S. Sherrington, a major founding figure in the study of

neuroscience, was the first to identify and describe the stretch

reflex. In trying to determine what parts of the brain were

responsible for movement, Sherrington conducted experiments

on rabbits and cats by operating on the brain. When he

transected the brain of a cat just above the level of the midbrain,

so that only the brain stem remained, the animal was incapable

of spontaneous action; yet it extended its limbs in an

exaggerated way and would stand indefinitely in forced

extension until it was knocked over––a condition he called

decerebrate rigidity. Furthermore, trying to flex the cat’s limbs

heightened the contraction of the muscles so that the leg

forcibly resisted his efforts.1 His experiments demonstrated

three things: First, the exaggerated extension of the limbs was

not caused by the voluntary part of the brain, but by automatic,

constant signals from the brain stem that maintained tone in the

limbs––what Sherrington called tonic activity, and which he

distinguished from more active contraction of muscles.2 This

concept of constant, low-level tone in muscles is still widely

accepted today.

Second, when he tried to flex the decerebrate animal’s

limb, the resistance to flexion indicated that receptors in the

muscles themselves must be activating the muscles that

extended the limb, which meant that the main source of this

activity must be proprioceptive outflow from stretch receptors

in the muscles.3

Third, these stretch reflexes clearly played a role in

maintaining posture, since the extended limbs were resistant to

buckling at the joints and therefore helped to maintain the

animal’s upright support against gravity.

It is important to mention that the stretch reflexes are not

confined to the extensor muscles that keep our joints from

buckling. In fact, stretch reflexes act on virtually all the

different parts of the body, helping to maintain its stability. For

instance, the shoulder girdle is supported by muscles acting

upon it from various directions. Even freely hanging arms and

hands, which do not seem to need postural support, have

background tone that is maintained by stretch reflexes. In this

sense, every part of the body participates in postural support––

the arms, hands, and face no less than the legs and back.

Sherrington found that stretching a muscle not only caused

the muscle to resist the buckling of the limb by contracting, but

also caused related muscles to contract and support the activity

of the extended limb. At the same time, activity in the

antagonistic or opposing muscles was inhibited or prevented––a

phenomenon he called reciprocal innervation.4 Although the

stretch reflex forms a simple reflex arc, it is wired up to similar

and opposing groups of muscles so that, even at the spinal cord

level, the coordination of the reflex begins to get rather

complex (Fig. 3).

Fig. 3. The spinal circuits in the stretch reflex system at the

elbow: a. motor neuron to same (homonymous) muscle; b. motor

neuron to related (synergistic) muscles; c. inhibition of motor

neuron to opposing (antagonistic) muscle

Since all this was discovered many years ago, we have

learned much more about posture and reflexes. T.D.M. Roberts,

for instance, points out that balance is maintained not only by

automatic stretch reflexes, but also by anticipatory and learned

responses,5 which play an important role in posture and support.

But underlying all of these responses are stretch reflexes, which

are operating constantly throughout the body as the basic

functional unit of the postural system. As we have seen, these

reflexes are wired at the spinal cord level so that even the


higher functions are built upon and work in conjunction with

stretch reflexes, adjusting some and turning off others to

produce a wide variety of voluntary movements in the context

of postural support. Basically our complex neural wiring

involving muscle spindles, afferent nerves, spinal cord, and

motor nerves keeps the whole body taut and the limbs engaged

but flexible and fluid when necessary, like the strings of a

marionette. The higher centers of the nervous system––the brain

stem, cortex, and cerebellum––work with and build upon these

circuits.

The entire muscle system, then, is invested with sensors

that play a crucial part in our postural support by enabling

muscles to sense changes in length and send messages that, in

turn, trigger muscle activity designed to counteract these

changes in length and maintain postural tone. Coupled with the

elastic and energy-storing potential of muscle tissue, the stretch

reflex system converts the musculoskeletal structure into a

spring-like framework capable of automatically supporting the

body against gravity and stabilizing all the parts of the body in

movement.

Muscles Spindles and the Reflex Arc

How do stretch reflexes work? We saw a moment ago that

stretch reflexes operate as a reflex arc that begins with a sensory

signal sent by a stretch receptor in the muscle. The stretch

receptor, called a muscle spindle, is an amazing little organ

(Fig. 4a.). It is called a muscle spindle because of its

resemblance to a textile spindle; that is, it is shaped like a

cylinder that bulges at the middle and tapers toward the ends.

Fig. 4a. Muscle spindles located on the main muscle fibers

The spindle is made up of a bundle of very tiny contractile

muscle fibers––about three to ten in number––that attach where

they taper at each end to the connective tissue that binds

together the fibers of the main muscle. These tiny fibers,

sometimes called intrafusal fibers to distinguish them from the

extrafusal fibers that make up the main muscle, are much

smaller in diameter and length than the extrafusal fibers––they

are only four to ten mm in length.

Wrapping around the muscle spindle is an afferent nerve

that carries sensory information to the spinal cord. The part that

wraps around the spindle is called an “annulospiral” receptor

because of its shape (Fig. 4b.). When the larger muscle fibers

are stretched this also stretches the intrafusal fibers that make

up the muscle spindle and elongates the annulospiral receptor

endings wrapped around it. This activates the nerve, which

sends an impulse to the spinal cord, where it synapses with the

motor nerve innervating the same muscle, telling the muscle to

contract. In this way, the muscle spindle functions as a very

sensitive organ for detecting changes in the length of a muscle

and sending an impulse to the spine, which in turn “reflects

back” a motor impulse to the same muscle.

Fig. 4b. Annulospiral receptor wrapping around the

intrafusal fibers that make up the muscle spindle

This reflex arc operates as a negative feedback loop. When,

for instance, we are standing and our knees buckle from the

force of gravity, this buckling stretches the quadriceps muscle,

which stretches the muscle spindle, activating the annulospiral

receptor wrapped around the spindle, which sends impulses to

the spine and synapses with motor nerves that, in turn, tell the

quadriceps muscle to contract. This muscular contraction

reduces stretch on the spindle so that the annulospiral receptor

stops firing––a negative loop that is turned on by stretch and

stopped when the muscle contracts and the spindle is no longer

being stretched. This feedback loop thus operates continuously

to maintain stability in the joints (Fig. 5 ).


AmSAT Journal / Fall 2013 / Issue No. 4 www.AmSATonline.org 19

Antagonistic Action and Stretch Reflexes

But this stretch reflex system cannot work properly if the

muscular system is not working efficiently. In Part 1, we saw

that the musculoskeletal structure can be described as a system

of tensile components and struts in which the tensile

components support the struts, but the struts maintain length on

the tensile components. If this system is interfered with––in

other words, if we tighten the neck and interfere with head

balance so that the back muscles are shortened––muscles

throughout the body must compensate to maintain upright

support. When this happens, the muscles can no longer lengthen

and the spindles no longer register stretch. Parts of the stretch

reflex system, quite literally, shut down.

When this situation occurs, the remedy is to restore length

to the system. This can be achieved by placing the skeleton in

supportive positions in order to restore length to particular

muscle groups that have forgotten how to maintain length and

perform their supportive function. This restores natural

tensegrity support and increases the stored potential energy in

muscles, which imparts more spring and elasticity to the

framework. But because the tensegrity system is invested with

sensors that register stretch, restoring muscle length also has an

effect on the stretch reflex system. Stretch reflexes that

previously were not operative begin to work, the body begins to

feel lighter, the spine regains a kind of inward buoyancy, and

muscles that were flaccid and tight spontaneously tone up and

release. These changes in the musculoskeletal system can be

observed and felt from head to toe. We begin, as we say, to “go

up.”

What has happened is that the condition of elasticity and

release in muscles, which is part of the tensegrity design, has

stimulated stretch reflexes. We might assume, because muscle

spindles are capable of adjusting to the shortened condition of

muscles, that the stretch reflex is always operative. However,

when muscles become too shortened, the spindles cannot adjust

and the stretch reflexes shut down. To work properly, the

stretch reflexes require both the elasticity of muscles and the

dynamic relationships between muscles and bones that are

established when the system works as a whole. Without these

conditions, the reflexes are inoperative; when these conditions

are restored, the stretch reflexes are stimulated, and the

muscular system regains its automatic, buoyant support.

Stretch reflexes, then, do not work independently of the

condition of muscles, but only function properly when muscles

are elastically supporting the skeleton. If this network is not

operating elastically, the muscular support system is not

properly activated, and effortless support is replaced with

chronic contraction of muscles, which are now needed to

maintain upright posture; some stretch reflexes end up operating

in a compensatory mode and many do not operate at all. When

the system is restored, the stretch reflexes are activated, muscles

no longer need to forcibly contract, and muscles perform their

naturally supportive function with more length and tone. In

short, elasticity in the context of the architectural whole is the

key to the stretch reflexes operating effectively to provide

muscular support of the whole with a minimum of effort.

Stretch Reflexes and Muscle Tone

Knowing how stretch reflexes work is essential to

understanding what makes muscles healthy. In Part 1, we saw

that we cannot describe a muscle as being healthy in the

absence of elasticity. A muscle is certainly not healthy simply

because it is built up and can perform work or because it is

relaxed and can be mechanically stretched. For muscle tissue to

be healthy, there must be an active relationship between length

and tension. For the stretch reflex system to operate fully, and

for muscles to contract most effectively, they must function

antagonistically within the context of a skeletal framework that

imposes stretch so that the muscle spindles can sensitively

register changes in muscle length and respond with a lively,

spring-like activity. This is a key part of what makes muscles

healthy and toned.


Fig. 5. Negative feedback loop of the stretch reflex arc: a. flexor muscles keep the arm flexed at the elbow; b.

muscle is stretched, muscle spindle fires and activates reflex arc; c. motor neuron fires, muscle contracts, spindle

is no longer stretched and stops firing


An Alexander Technique teacher can detect the presence of

this lively tone and the life in the muscle. This is not just

fanciful or metaphorical. It is an observable condition in which

muscles are lengthening, the spindles are firing, and the

contractile components of the muscles maintain a healthy

amount of resistance against lengthening—in other words,

underlying electrical and chemical activity combines with an

elastic component to produce an overall lively, flexible quality

in the muscle that can be felt. And it cannot be achieved

through any sort of treatment, bodywork, or exercise, but only

in the context of active support and movement in the

gravitational field.

The Alexander Technique

Understanding this principle of muscle function was one of

Alexander’s great accomplishments. Fully one half of the

Alexander work is about restoring the postural/stretch system to

its normal working; the other half is about gaining conscious

control over this system so that we

can apply this knowledge in our daily

activities. When we are born, skeletal

support imparts a natural length to

our muscles so that our inborn,

natural reflexes can respond to

stretch all over the body, making it

possible for the system to provide

support in an efficient and effortless

way. Habitual tightening of muscles

however––as well as other influences in life––begin to interfere

with this system, and the body has no other alternative but to

maintain support by replacing stretch with muscle tension. At

first, this may not be a problem; but over time, the

compensations become chronic and the muscles do not have the

length they need for the stretch reflexes to be activated. We are

then faced with the dual disaster of losing tone in many of the

muscles needed to support the body against gravity, and other

muscles working far too much and becoming chronically tight.

The body cannot find a way to recover and the postural system

cannot work correctly. New activities, meanwhile, are

undertaken in an increasingly harmful way until, with time,

dysfunction and collapse result. This disarrangement is most

easily seen in the pulling back of the head, the shortening of the

spine, the overworking of the lower part of the back, and

collapse of other parts of the body. The antagonistic stretch on

the muscles is compromised, the stretch reflex system cannot

work properly, and the system, unable to work as it is designed

to work, goes into collapse and fixation.

It is at this point that re-educational work is needed,

beginning with some form of mechanical support (such as

sitting with a supported back or lying in a semi-supine

position). The idea is to restore the stretch reflex system,

including the ability of muscle to sensitively register changes in

length, which is a big part of their function––and a big part of

what the Alexander Technique is all about. One option is to

address this by stretching and strengthening muscles, but this

will not work, because the system is designed to work as a

whole, with muscles functioning antagonistically in the context

of postural support. No amount of strengthening, exercising,

relaxing, or balancing muscles can restore this condition when

the system is so maladjusted and sensory input so distorted.

Because the system works as a whole, it cannot be put together

piecemeal by trying to correct one part or another; all the parts

must be readjusted in relation to gravity as an interrelated

whole.

Reciprocity of Nerves and Body

Although neuroscientists have explained a great deal about

how muscles spindles work, their work has not yet taken into

account the functioning of the body as a whole. When we

consider the reflex arc, it is easy to assume that it is basically a

two-way street—a sensory response to stretch in muscle

followed by a motor impulse that is reflected back to the

muscle. But in order to work properly, muscle spindles must

operate in the context of a system of muscle pulls and stretches

that maintain the proper organic conditions under which the

muscle spindles are at their most sensitive and the muscles at

their most healthy and responsive. Stretch reflexes are designed

to respond automatically to stretch, but they function as part of

the dynamic interplay between the

signaling to and from muscles and

the state of the musculoskeletal

system as a whole and cannot be

expected to work normally if this

system is imbalanced.

One of the things this shows is

that awareness alone cannot improve

muscular and motor functioning. We

often hear Alexander Technique

spoken of as a kinesthetic method, which of course it is. Other

methods, such as Feldenkrais and relaxation techniques, also

utilize kinesthetic awareness to reduce unnecessary muscle

tension. We receive proprioceptive information from muscle

spindles, but if muscles are chronically tight, this information is

drastically reduced and less accurate. This means that unless we

establish lengthening of muscles as a precondition for healthful

function, trying to be aware of muscles is virtually useless, not

to mention misleading. Before we can rely on kinesthetic input,

we must first restore length to muscles and, as much as

possible, remove the interferences with normal and natural

muscle tone. Awareness is not the first step in the process––it

depends on basic organic conditions of elasticity in muscles,

which is why awareness must be based on re-education.

Summary

To summarize, the body is organized as a tensegrity

structure; stretch reflexes convert this structure into a spring-

like framework. Essential to this system is the elastic condition

of the muscles that erect the tensegrity structure, so that all the

muscles, tendons, and ligaments––the tensile parts of the

system, the guy wires––perform work appropriately and the

workload is distributed across the whole network. This

elasticity imparts potential energy to the muscles, since muscles

store energy when they are lengthened; the resulting rebound

effect helps to maintain the integrity of the system.

Loss of length in muscle means that the structure cannot

support itself properly, with the result that various guy wires

take on too much load; it also means loss of spring-like support

and potential energy in muscle. We experience this in the

heaviness and stiffness in our legs as we age, in contrast to the

spring-like legs of children.


“The idea is to restore the stretch reflex

system, including the ability of muscle

to sensitively register changes in length,

which is a big part of their function––and

a big part of what the Alexander

Technique is all about.”

Continued on page 22.


At the same time, muscles must maintain tone to stabilize

the tensegrity structure, which is made possible by the stretch

reflex system. This system can only work efficiently when

length is restored to muscles, which stimulates their reflex

activity. The antagonistic action of muscles, then, is the

condition under which the stretch reflex system operates to best

advantage. In the next installment in this four part series, we

will look at the role of the head and trunk in organizing the

working of this system as a whole.

Endnotes

1. See Sir Charles Sherrington, The Integrative Action of the

Nervous System (New Haven, CT: Yale University Press,

1961), 299–302.

2. Speaking of extensor activity in the decerebrate animal,

Sherrington writes: “These muscles counteract a force (gravity)

that continually threatens to upset the natural posture. The force

acts continuously and the muscles exhibit continued action,

tonus” (Integrative Action, 302). He later continues: “Two

separable systems of motor innervation appear thus controlling

two sets of musculature: one system exhibits those transient

phases of heightened reaction which constitute reflex

movements; the other maintains that steady tonic response

which supplies the muscular contractions necessary to

attitude” (Ibid.).

3. Sherrington, Integrative Action, 337: “[I]n the decerebrate

dog the tonic extensor rigidity of the leg appears reflexly

maintained by afferent neurones reaching the cord from the

deep structures of the leg itself. Similarly, if the knee-jerk be

accepted as evidence in the spinal animal of a spinal tonus in

the extensor muscle, this tonus seems maintained by afferent

fibres from the extensor muscle itself, since the knee-jerk is

extinguished by severance of those fibres.”

4. Ibid., 86–100.

5. See Tristan D. M. Roberts, Understanding Balance: The

Mechanics of Posture and Locomotion (London: Chapman &

Hall, 1995); see also Tristan D. M. Roberts, “Reflexes, Habits

and Skills.” Direction–A Journal on the Alexander Technique,

no. 10, 23–28.

Drawings by Helen Leshinsky.

Dr. Theodore (Ted) Dimon received M.A. and Ed.D degrees in

Education from Harvard University and Alexander Technique

teacher certification from Walter Carrington. Dimon is the author

of five books: Anatomy of the Moving Body; The Body in Motion;

Your Body, Your Voice; The Elements of Skill; and The

Undivided Self. He is the founder and director of The Dimon

Institute in New York City and an adjunct professor of Education

and Psychology at Teachers College, Columbia University. More

information about Dimon’s work and The Dimon Institute can be

found at: www.dimoninstitute.org.

© 2013 Theodore Dimon. All rights reserved.

Photograph of Ted Dimon by Marie-France Drouet.

The Organization of Movement, continued from page 20.

Documents

The Organization of Movement Four Talks on the …...muscle through the peripheral nerves or originate higher up in the brain and travel down to these peripheral nerves. In any The