*********************************************
STRETCHING AND FLEXIBILITY:
Everything you never wanted to know
(Part 1 of 4)
*********************************************
by Brad Appleton
Version: 1.27, Last Modified 95/05/19
Copyright (C) 1993, 1994, 1995 by Bradford D. Appleton
Permission is granted to make and distribute verbatim copies of this
document provided the copyright notice and this permission notice are
preserved on all copies.
This document is available in ascii, texinfo, postscript, dvi, and html
formats via anonymous ftp from the host `cs.huji.ac.il'. Look under the
directory `/pub/doc/faq/rec/martial.arts'. The file name matches the
wildcard pattern `stretching.*'. The file suffix indicates the format.
For WWW users, the URL is:
http://www.cs.huji.ac.il/papers/rma/stretching_toc.html.
------------------------------
Subject: What's New This Month
There are no changes this month. However, I am looking for a new
anonymous FTP site at which to archive this FAQ in its available
formats. Please send me e-mail if you know of or can provide such a
site.
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Subject: Table of Contents
All section titles in this document begin with the prefix "Subject: ". If
you wish, you may scan ahead to a particular section by searching for the
regular expression /^Subject: SECTION-NAME/. For example, to go to the
unnumbered section named "Introduction", you could scan for
/^Subject: Intro/; to go to section 1.1, you could scan for
/^Subject: 1\.1/; and to go to appendix A, you could scan for
/^Subject: Appendix A/.
This document is organized into the following sections:
PART 1:
Introduction
Disclaimer
Acknowledgements
About the Author
1 - Physiology of Stretching
1.1 - The Musculoskeletal System
1.2 - Muscle Composition
1.2.1 - How Muscles Contract
1.2.2 - Fast and Slow Muscle Fibers
1.3 - Connective Tissue
1.4 - Cooperating Muscle Groups
1.5 - Types of Muscle Contractions
1.6 - What Happens When You Stretch
1.6.1 - Proprioceptors
1.6.2 - The Stretch Reflex
1.6.2.1 - Components of the Stretch Reflex
1.6.3 - The Lengthening Reaction
1.6.4 - Reciprocal Inhibition
PART 2:
2 - Flexibility
2.1 - Types of Flexibility
2.2 - Factors Limiting Flexibility
2.2.1 - How Connective Tissue Affects Flexibility
2.2.2 - How Aging Affects Flexibility
2.3 - Strength and Flexibility
2.3.1 - Why Bodybuilders Should Stretch
2.3.2 - Why Contortionists Should Strengthen
2.4 - Overflexibility
3 - Types of Stretching
3.1 - Ballistic Stretching
3.2 - Dynamic Stretching
3.3 - Active Stretching
3.4 - Passive Stretching
3.5 - Static Stretching
3.6 - Isometric Stretching
3.6.1 - How Isometric Stretching Works
3.7 - PNF Stretching
3.7.1 - How PNF Stretching Works
PART 3:
4 - How to Stretch
4.1 - Warming Up
4.1.1 - General Warm-Up
4.1.1.1 - Joint Rotations
4.1.1.2 - Aerobic Activity
4.1.2 - Warm-Up Stretching
4.1.2.1 - Static Warm-Up Stretching
4.1.2.2 - Dynamic Warm-Up Stretching
4.1.3 - Sport-Specific Activity
4.2 - Cooling Down
4.3 - Massage
4.4 - Elements of a Good Stretch
4.4.1 - Isolation
4.4.2 - Leverage
4.4.3 - Risk
4.5 - Some Risky Stretches
4.6 - Duration, Counting, and Repetition
4.7 - Breathing During Stretching
4.8 - Exercise Order
4.9 - When to Stretch
4.9.1 - Early-Morning Stretching
4.10 - Stretching With a Partner
4.11 - Stretching to Increase Flexibility
4.12 - Pain and Discomfort
4.12.1 - Common Causes of Muscular Soreness
4.12.2 - Stretching with Pain
4.12.3 - Overstretching
4.13 - Performing Splits
4.13.1 - Common Problems When Performing Splits
4.13.2 - The Front Split
4.13.3 - The Side Split
4.13.4 - Split-Stretching Machines
PART 4:
Appendix A - References on Stretching
A.1 - Recommendations
A.2 - Additional Comments
Appendix B - Working Toward the Splits
B.1 - lower back stretches
B.2 - lying buttock stretch
B.3 - groin and inner-thigh stretch
B.4 - seated leg stretches
B.4.1 - seated calf stretch
B.4.2 - seated hamstring stretch
B.4.3 - seated inner-thigh stretch
B.5 - psoas stretch
B.6 - quadricep stretch
B.7 - lying `V' stretch
Appendix C - Normal Ranges of Joint Motion
C.1 - Neck
C.2 - Lumbar Spine
C.3 - Shoulder
C.4 - Elbow
C.5 - Wrist
C.6 - Hip
C.7 - Knee
C.8 - Ankle
Index
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Subject: Introduction
This document is a modest attempt to compile a wealth of information in
order to answer some frequently asked questions about stretching and
flexibility. It is organized into chapters covering the following topics:
1. Physiology of Stretching
2. Flexibility
3. Types of Stretching
4. How to Stretch
Although each chapter may refer to sections in other chapters, it is not
required that you read every chapter in the order presented. It is
important, however, that you read the disclaimer before reading any other
sections of this document. (See "Disclaimer"). If you wish to skip around,
numerous cross references are supplied in each section to help you find the
concepts you may have missed. There is also an index at the end of this
document.
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Subject: Disclaimer
Although every effort has been made to ensure that all information
presented in this document is accurate, errors may still be present. If
you notice any errors, please send corrections via e-mail to
`Brad_Appleton@ivhs.mot.com'.
THE AUTHOR MAKES NO WARRANTY OF ANY KIND IN REGARD TO THE CONTENT OF THIS
DOCUMENT, INCLUDING, BUT NOT LIMITED TO, ANY IMPLIED WARRANTIES OF
MERCHANTABILITY, OR FITNESS FOR ANY PARTICULAR PURPOSE. THE AUTHOR OF THIS
DOCUMENT SHALL NOT BE LIABLE FOR ERRORS CONTAINED IN IT, OR FOR INCIDENTAL
OR CONSEQUENTIAL DAMAGES IN CONNECTION WITH THE FURNISHING OF, USE OF, OR
RELIANCE UPON INFORMATION CONTAINED IN THIS DOCUMENT.
In other words: "I'm not a doctor, nor do I play one on TV!" I can not be
held liable for any damages or injuries that you might suffer from somehow
relying upon information in this document, no matter how awful. Not even if
the information in question is incorrect or inaccurate.
------------------------------
Subject: Acknowledgements
Thanks to all the readers of the `rec.martial-arts', `rec.arts.dance' and
`misc.fitness' newsgroups on Usenet who responded to my request for
questions (and answers) on stretching. Many parts of this document come
directly from these respondents. Thanks in particular to Shawne Neeper for
sharing her formidable knowledge of muscle anatomy and physiology.
Other portions of this document have been taken from the following books:
`Sport Stretch', by Michael J. Alter
(referred to as M. Alter in the rest of this document)
`Stretching Scientifically', by Tom Kurz
(referred to as Kurz in the rest of this document)
`SynerStretch For Total Body Flexibility', from Health For Life
(referred to as `SynerStretch' in the rest of this document)
`The Health For Life Training Advisor', also from Health For Life
(referred to as `HFLTA' in the rest of this document)
`Mobility Training for the Martial Arts', by Tony Gummerson
(referred to as Gummerson in the rest of this document)
Further information on these books and others, is available near the end of
this document. (See "Appendix A - References on Stretching").
------------------------------
Subject: About the Author
I am *not* an expert in anatomy or physiology! I do have over 6 years of
martial arts training, and over 20 years of dance training in classical
ballet, modern, and jazz. However, my primary "qualifications" to write
this document are that I took considerable time and effort to read several
books on the topic, and to combine the information that I read with the
information supplied to me from many knowledgeable readers of Usenet news.
I have tried to write this document for all audiences and not make it
specific to any particular sport or art (such as dancing or martial arts). I
have also tried to leave out any of my own personal opinions or feelings
and just state the facts as related to me by the *real* experts.
I am always interested in hearing about any new information which would be
appropriate to add to this document. If you have any such information about
a stretching technique, a book, or anything else you can think of, please
feel free to contact me. All I ask is that you be prepared to provide me
with at least one reputable and reliable source for your information.
------------------------------
Subject: 1 - Physiology of Stretching
The purpose of this chapter is to introduce you to some of the basic
physiological concepts that come into play when a muscle is stretched.
Concepts will be introduced initially with a general overview and then (for
those who want to know the gory details) will be discussed in further
detail. If you aren't all that interested in this aspect of stretching, you
can skip this chapter. Other sections will refer to important concepts from
this chapter and you can easily look them up on a "need to know" basis.
------------------------------
Subject: 1.1 - The Musculoskeletal System
Together, muscles and bones comprise what is called the "musculoskeletal
system" of the body. The bones provide posture and structural support for
the body and the muscles provide the body with the ability to move (by
contracting, and thus generating tension). The musculoskeletal system also
provides protection for the body's internal organs. In order to serve their
function, bones must be joined together by something. The point where bones
connect to one another is called a "joint", and this connection is made
mostly by "ligaments" (along with the help of muscles). Muscles are
attached to the bone by "tendons". Bones, tendons, and ligaments do not
possess the ability (as muscles do) to make your body move. Muscles are
very unique in this respect.
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Subject: 1.2 - Muscle Composition
Muscles vary in shape and in size, and serve many different purposes. Most
large muscles, like the hamstrings and quadriceps, control motion. Other
muscles, like the heart, and the muscles of the inner ear, perform other
functions. At the microscopic level however, all muscles share the same
basic structure.
At the highest level, the (whole) muscle is composed of many strands of
tissue called "fascicles". These are the strands of muscle that we see when
we cut red meat or poultry. Each fascicle is composed of "fasciculi" which
are bundles of "muscle fibers". The muscle fibers are in turn composed of
tens of thousands of thread-like "myofybrils", which can contract, relax,
and elongate (lengthen). The myofybrils are (in turn) composed of up to
millions of bands laid end-to-end called "sarcomeres". Each sarcomere is
made of overlapping thick and thin filaments called "myofilaments". The
thick and thin myofilaments are made up of "contractile proteins",
primarily actin and myosin.
------------------------------
Subject: 1.2.1 - How Muscles Contract
The way in which all these various levels of the muscle operate is as
follows: Nerves connect the spinal column to the muscle. The place where
the nerve and muscle meet is called the "neuromuscular junction". When an
electrical signal crosses the neuromuscular junction, it is transmitted
deep inside the muscle fibers. Inside the muscle fibers, the signal
stimulates the flow of calcium which causes the thick and thin myofilaments
to slide across one another. When this occurs, it causes the sarcomere to
shorten, which generates force. When billions of sarcomeres in the muscle
shorten all at once it results in a contraction of the entire muscle fiber.
When a muscle fiber contracts, it contracts completely. There is no such
thing as a partially contracted muscle fiber. Muscle fibers are unable to
vary the intensity of their contraction relative to the load against which
they are acting. If this is so, then how does the force of a muscle
contraction vary in strength from strong to weak? What happens is that
more muscle fibers are recruited, as they are needed, to perform the job at
hand. The more muscle fibers that are recruited by the central nervous
system, the stronger the force generated by the muscular contraction.
------------------------------
Subject: 1.2.2 - Fast and Slow Muscle Fibers
The energy which produces the calcium flow in the muscle fibers comes from
"mitochondria", the part of the muscle cell that converts glucose (blood
sugar) into energy. Different types of muscle fibers have different amounts
of mitochondria. The more mitochondria in a muscle fiber, the more energy
it is able to produce. Muscle fibers are categorized into "slow-twitch
fibers" and "fast-twitch fibers". Slow-twitch fibers (also called "Type 1
muscle fibers") are slow to contract, but they are also very slow to
fatigue. Fast-twitch fibers are very quick to contract and come in two
varieties: "Type 2A muscle fibers" which fatigue at an intermediate rate,
and "Type 2B muscle fibers" which fatigue very quickly. The main reason the
slow-twitch fibers are slow to fatigue is that they contain more
mitochondria than fast-twitch fibers and hence are able to produce more
energy. Slow-twitch fibers are also smaller in diameter than fast-twitch
fibers and have increased capillary blood flow around them. Because they
have a smaller diameter and an increased blood flow, the slow-twitch fibers
are able to deliver more oxygen and remove more waste products from the
muscle fibers (which decreases their "fatigability").
These three muscle fiber types (Types 1, 2A, and 2B) are contained in all
muscles in varying amounts. Muscles that need to be contracted much of the
time (like the heart) have a greater number of Type 1 (slow) fibers.
According to `HFLTA':
When a muscle begins to contract, primarily Type 1 fibers are activated
first, then Type 2A, then 2B. This sequence of fiber recruitment allows
very delicate and finely tuned muscle responses to brain commands. It
also makes Type 2B fibers difficult to train; most of the Type 1 and 2A
fibers have to be activated already before a large percentage of the 2B
fibers participate.
`HFLTA' further states that the the best way to remember the difference
between muscles with predominantly slow-twitch fibers and muscles with
predominantly fast-twitch fibers is to think of "white meat" and "dark
meat". Dark meat is dark because it has a greater number of slow-twitch
muscle fibers and hence a greater number of mitochondria, which are dark.
White meat consists mostly of muscle fibers which are at rest much of the
time but are frequently called on to engage in brief bouts of intense
activity. This muscle tissue can contract quickly but is fast to fatigue
and slow to recover. White meat is lighter in color than dark meat because
it contains fewer mitochondria.
------------------------------
Subject: 1.3 - Connective Tissue
Located all around the muscle and its fibers are "connective tissues".
Connective tissue is composed of a base substance and two kinds of protein
based fiber. The two types of fiber are "collagenous connective tissue" and
"elastic connective tissue". Collagenous connective tissue consists mostly
of collagen (hence its name) and provides tensile strength. Elastic
connective tissue consists mostly of elastin and (as you might guess from
its name) provides elasticity. The base substance is called
"mucopolysaccharide" and acts as both a lubricant (allowing the fibers to
easily slide over one another), and as a glue (holding the fibers of the
tissue together into bundles). The more elastic connective tissue there is
around a joint, the greater the range of motion in that joint. Connective
tissues are made up of tendons, ligaments, and the fascial sheaths that
envelop, or bind down, muscles into separate groups. These fascial
sheaths, or "fascia", are named according to where they are located in the
muscles:
"endomysium"
The innermost fascial sheath that envelops individual muscle fibers.
"perimysium"
The fascial sheath that binds groups of muscle fibers into individual
fasciculi (See "1.2 - Muscle Composition").
"epimysium"
The outermost fascial sheath that binds entire fascicles (See "1.2 -
Muscle Composition").
These connective tissues help provide suppleness and tone to the muscles.
------------------------------
Subject: 1.4 - Cooperating Muscle Groups
When muscles cause a limb to move through the joint's range of motion, they
usually act in the following cooperating groups:
"agonists"
These muscles cause the movement to occur. They create the normal range
of movement in a joint by contracting. Agonists are also referred to
as "prime movers" since they are the muscles that are primarily
responsible for generating the movement.
"antagonists"
These muscles act in opposition to the movement generated by the
agonists and are responsible for returning a limb to its initial
position.
"synergists"
These muscles perform, or assist in performing, the same set of joint
motion as the agonists. Synergists are sometimes referred to as
"neutralizers" because they help cancel out, or neutralize, extra
motion from the agonists to make sure that the force generated works
within the desired plane of motion.
"fixators"
These muscles provide the necessary support to assist in holding the
rest of the body in place while the movement occurs. Fixators are also
sometimes called "stabilizers".
As an example, when you flex your knee, your hamstring contracts, and, to
some extent, so does your gastrocnemius (calf) and lower buttocks.
Meanwhile, your quadriceps are inhibited (relaxed and lengthened somewhat)
so as not to resist the flexion (See "1.6.4 - Reciprocal Inhibition"). In
this example, the hamstring serves as the agonist, or prime mover; the
quadricep serves as the antagonist; and the calf and lower buttocks serve
as the synergists. Agonists and antagonists are usually located on
opposite sides of the affected joint (like your hamstrings and quadriceps,
or your triceps and biceps), while synergists are usually located on the
same side of the joint near the agonists. Larger muscles often call upon
their smaller neighbors to function as synergists.
The following is a list of commonly used agonist/antagonist muscle pairs:
* pectorals/latissimus dorsi (pecs and lats)
* anterior deltoids/posterior deltoids (front and back shoulder)
* trapezius/deltoids (traps and delts)
* abdominals/spinal erectors (abs and lower-back)
* left and right external obliques (sides)
* quadriceps/hamstrings (quads and hams)
* shins/calves
* biceps/triceps
* forearm flexors/extensors
------------------------------
Subject: 1.5 - Types of Muscle Contractions
The contraction of a muscle does not necessarily imply that the muscle
shortens; it only means that tension has been generated. Muscles can
contract in the following ways:
"isometric contraction"
This is a contraction in which no movement takes place, because the
load on the muscle exceeds the tension generated by the contracting
muscle. This occurs when a muscle attempts to push or pull an
immovable object.
"isotonic contraction"
This is a contraction in which movement *does* take place, because the
tension generated by the contracting muscle exceeds the load on the
muscle. This occurs when you use your muscles to successfully push or
pull an object.
Isotonic contractions are further divided into two types:
"concentric contraction"
This is a contraction in which the muscle decreases in length
(shortens) against an opposing load, such as lifting a weight up.
"eccentric contraction"
This is a contraction in which the muscle increases in length
(lengthens) as it resists a load, such as pushing something down.
During a concentric contraction, the muscles that are shortening serve
as the agonists and hence do all of the work. During an eccentric
contraction the muscles that are lengthening serve as the agonists
(and do all of the work). (See "1.4 - Cooperating Muscle Groups").
------------------------------
Subject: 1.6 - What Happens When You Stretch
The stretching of a muscle fiber begins with the sarcomere (See "1.2 -
Muscle Composition"), the basic unit of contraction in the muscle fiber.
As the sarcomere contracts, the area of overlap between the thick and thin
myofilaments increases. As it stretches, this area of overlap decreases,
allowing the muscle fiber to elongate. Once the muscle fiber is at its
maximum resting length (all the sarcomeres are fully stretched), additional
stretching places force on the surrounding connective tissue (See "1.3 -
Connective Tissue"). As the tension increases, the collagen fibers in the
connective tissue align themselves along the same line of force as the
tension. Hence when you stretch, the muscle fiber is pulled out to its full
length sarcomere by sarcomere, and then the connective tissue takes up the
remaining slack. When this occurs, it helps to realign any disorganized
fibers in the direction of the tension. This realignment is what helps to
rehabilitate scarred tissue back to health.
When a muscle is stretched, some of its fibers lengthen, but other fibers
may remain at rest. The current length of the entire muscle depends upon
the number of stretched fibers. According to `SynerStretch':
Picture little pockets of fibers distributed throughout the muscle body
stretching, and other fibers simply going along for the ride. Just as
the total strength of a contracting muscle is a result of the number of
fibers contracting, the total length of a stretched muscle is a result
of the number of fibers stretched - the more fibers stretched, the more
length developed by the muscle for a given stretch.
------------------------------
Subject: 1.6.1 - Proprioceptors
The nerve endings that relay all the information about the musculoskeletal
system to the central nervous system are called "proprioceptors".
Proprioceptors (also called "mechanoreceptors") are the source of all
"proprioception": the perception of one's own body position and movement.
The proprioceptors detect any changes in physical displacement (movement or
position) and any changes in tension, or force, within the body. They are
found in all nerve endings of the joints, muscles, and tendons. The
proprioceptors related to stretching are located in the tendons and in the
muscle fibers.
There are two kinds of muscle fibers: "intrafusal muscle fibers" and
"extrafusal muscle fibers". Extrafusil fibers are the ones that contain
myofibrils (See "1.2 - Muscle Composition") and are what is usually meant
when we talk about muscle fibers. Intrafusal fibers are also called "muscle
spindles" and lie parallel to the extrafusal fibers. Muscle spindles, or
"stretch receptors", are the primary proprioceptors in the muscle. Another
proprioceptor that comes into play during stretching is located in the
tendon near the end of the muscle fiber and is called the "golgi tendon
organ". A third type of proprioceptor, called a "pacinian corpuscle", is
located close to the golgi tendon organ and is responsible for detecting
changes in movement and pressure within the body.
When the extrafusal fibers of a muscle lengthen, so do the intrafusal
fibers (muscle spindles). The muscle spindle contains two different types
of fibers (or stretch receptors) which are sensitive to the change in
muscle length and the rate of change in muscle length. When muscles
contract it places tension on the tendons where the golgi tendon organ is
located. The golgi tendon organ is sensitive to the change in tension and
the rate of change of the tension.
------------------------------
Subject: 1.6.2 - The Stretch Reflex
When the muscle is stretched, so is the muscle spindle (See "1.6.1 -
Proprioceptors"). The muscle spindle records the change in length (and how
fast) and sends signals to the spine which convey this information. This
triggers the "stretch reflex" (also called the "myotatic reflex") which
attempts to resist the change in muscle length by causing the stretched
muscle to contract. The more sudden the change in muscle length, the
stronger the muscle contractions will be (plyometric, or "jump", training
is based on this fact). This basic function of the muscle spindle helps to
maintain muscle tone and to protect the body from injury.
One of the reasons for holding a stretch for a prolonged period of time is
that as you hold the muscle in a stretched position, the muscle spindle
habituates (becomes accustomed to the new length) and reduces its
signaling. Gradually, you can train your stretch receptors to allow
greater lengthening of the muscles.
Some sources suggest that with extensive training, the stretch reflex of
certain muscles can be controlled so that there is little or no reflex
contraction in response to a sudden stretch. While this type of control
provides the opportunity for the greatest gains in flexibility, it also
provides the greatest risk of injury if used improperly. Only consummate
professional athletes and dancers at the top of their sport (or art) are
believed to actually possess this level of muscular control.
------------------------------
Subject: 1.6.2.1 - Components of the Stretch Reflex
The stretch reflex has both a dynamic component and a static component.
The static component of the stretch reflex persists as long as the muscle
is being stretched. The dynamic component of the stretch reflex (which can
be very powerful) lasts for only a moment and is in response to the initial
sudden increase in muscle length. The reason that the stretch reflex has
two components is because there are actually two kinds of intrafusal muscle
fibers: "nuclear chain fibers", which are responsible for the static
component; and "nuclear bag fibers", which are responsible for the dynamic
component.
Nuclear chain fibers are long and thin, and lengthen steadily when
stretched. When these fibers are stretched, the stretch reflex nerves
increase their firing rates (signaling) as their length steadily increases.
This is the static component of the stretch reflex.
Nuclear bag fibers bulge out at the middle, where they are the most
elastic. The stretch-sensing nerve ending for these fibers is wrapped
around this middle area, which lengthens rapidly when the fiber is
stretched. The outer-middle areas, in contrast, act like they are filled
with viscous fluid; they resist fast stretching, then gradually extend
under prolonged tension. So, when a fast stretch is demanded of these
fibers, the middle takes most of the stretch at first; then, as the
outer-middle parts extend, the middle can shorten somewhat. So the nerve
that senses stretching in these fibers fires rapidly with the onset of a
fast stretch, then slows as the middle section of the fiber is allowed to
shorten again. This is the dynamic component of the stretch reflex: a
strong signal to contract at the onset of a rapid increase in muscle
length, followed by slightly "higher than normal" signaling which gradually
decreases as the rate of change of the muscle length decreases.
------------------------------
Subject: 1.6.3 - The Lengthening Reaction
When muscles contract (possibly due to the stretch reflex), they produce
tension at the point where the muscle is connected to the tendon, where the
golgi tendon organ is located. The golgi tendon organ records the change in
tension, and the rate of change of the tension, and sends signals to the
spine to convey this information (See "1.6.1 - Proprioceptors"). When this
tension exceeds a certain threshold, it triggers the "lengthening reaction"
which inhibits the muscles from contracting and causes them to relax.
Other names for this reflex are the "inverse myotatic reflex", "autogenic
inhibition", and the "clasped-knife reflex". This basic function of the
golgi tendon organ helps to protect the muscles, tendons, and ligaments
from injury. The lengthening reaction is possible only because the
signaling of golgi tendon organ to the spinal cord is powerful enough to
overcome the signaling of the muscle spindles telling the muscle to
contract.
Another reason for holding a stretch for a prolonged period of time is to
allow this lengthening reaction to occur, thus helping the stretched
muscles to relax. It is easier to stretch, or lengthen, a muscle when it is
not trying to contract.
------------------------------
Subject: 1.6.4 - Reciprocal Inhibition
When an agonist contracts, in order to cause the desired motion, it usually
forces the antagonists to relax (See "1.4 - Cooperating Muscle Groups").
This phenomenon is called "reciprocal inhibition" because the antagonists
are inhibited from contracting. This is sometimes called "reciprocal
innervation" but that term is really a misnomer since it is the agonists
which inhibit (relax) the antagonists. The antagonists do *not* actually
innervate (cause the contraction of) the agonists.
Such inhibition of the antagonistic muscles is not necessarily required.
In fact, co-contraction can occur. When you perform a sit-up, one would
normally assume that the stomach muscles inhibit the contraction of the
muscles in the lumbar, or lower, region of the back. In this particular
instance however, the back muscles (spinal erectors) also contract. This is
one reason why sit-ups are good for strengthening the back as well as the
stomach.
When stretching, it is easier to stretch a muscle that is relaxed than to
stretch a muscle that is contracting. By taking advantage of the
situations when reciprocal inhibition *does* occur, you can get a more
effective stretch by inducing the antagonists to relax during the stretch
due to the contraction of the agonists. You also want to relax any muscles
used as synergists by the muscle you are trying to stretch. For example,
when you stretch your calf, you want to contract the shin muscles (the
antagonists of the calf) by flexing your foot. However, the hamstrings use
the calf as a synergist so you want to also relax the hamstrings by
contracting the quadricep (i.e., keeping your leg straight).
------------------------------
Brad_Appleton@ivhs.mot.com Motorola PNSB, Northbrook, IL USA
"And miles to go before I sleep." DISCLAIMER: I said it, not my employer!