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STRETCHING AND FLEXIBILITY:
Everything you never wanted to know
(Part 2 of 4)
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by Brad Appleton
Version: 1.27, Last Modified 95/05/19
Copyright (C) 1993, 1994, 1995 by Bradford D. Appleton
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Subject: Table of Contents for PART 2
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/.
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
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Subject: 2 - Flexibility
Flexibility is defined by Gummerson as "the absolute range of movement in a
joint or series of joints that is attainable in a momentary effort with the
help of a partner or a piece of equipment." This definition tells us that
flexibility is not something general but is specific to a particular joint
or set of joints. In other words, it is a myth that some people are
innately flexible throughout their entire body. Being flexible in one
particular area or joint does not necessarily imply being flexible in
another. Being "loose" in the upper body does not mean you will have a
"loose" lower body. Furthermore, according to `SynerStretch', flexibility
in a joint is also "specific to the action performed at the joint (the
ability to do front splits doesn't imply the ability to do side splits even
though both actions occur at the hip)."
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Subject: 2.1 - Types of Flexibility
Many people are unaware of the fact that there are different types of
flexibility. These different types of flexibility are grouped according to
the various types of activities involved in athletic training. The ones
which involve motion are called "dynamic" and the ones which do not are
called "static". The different types of flexibility (according to Kurz) are:
"dynamic flexibility"
Dynamic flexibility (also called "kinetic flexibility") is the ability
to perform dynamic (or kinetic) movements of the muscles to bring a
limb through its full range of motion in the joints.
"static-active flexibility"
Static-active flexibility (also called "active flexibility") is the
ability to assume and maintain extended positions using only the
tension of the agonists and synergists while the antagonists are being
stretched (See "1.4 - Cooperating Muscle Groups"). For example,
lifting the leg and keeping it high without any external support
(other than from your own leg muscles).
"static-passive flexibility"
Static-passive flexibility (also called "passive flexibility") is the
ability to assume extended positions and then maintain them using only
your weight, the support of your limbs, or some other apparatus (such
as a chair or a barre). Note that the ability to maintain the position
does not come solely from your muscles, as it does with static-active
flexibility. Being able to perform the splits is an example of
static-passive flexibility.
Research has shown that active flexibility is more closely related to the
level of sports achievement than is passive flexibility. Active
flexibility is harder to develop than passive flexibility (which is what
most people think of as "flexibility"); not only does active flexibility
require passive flexibility in order to assume an initial extended
position, it also requires muscle strength to be able to hold and maintain
that position.
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Subject: 2.2 - Factors Limiting Flexibility
According to Gummerson, flexibility (he uses the term "mobility") is
affected by the following factors:
* Internal influences
- the type of joint (some joints simply aren't meant to be flexible)
- the internal resistance within a joint
- bony structures which limit movement
- the elasticity of muscle tissue (muscle tissue that is scarred
due to a previous injury is not very elastic)
- the elasticity of tendons and ligaments (ligaments do not stretch
much and tendons should not stretch at all)
- the elasticity of skin (skin actually has some degree of
elasticity, but not much)
- the ability of a muscle to relax and contract to achieve the
greatest range of movement
- the temperature of the joint and associated tissues (joints and
muscles offer better flexibility at body temperatures that are 1
to 2 degrees higher than normal)
* External influences
- the temperature of the place where one is training (a warmer
temperature is more conducive to increased flexibility)
- the time of day (most people are more flexible in the afternoon
than in the morning, peaking from about 2:30pm-4pm)
- the stage in the recovery process of a joint (or muscle) after
injury (injured joints and muscles will usually offer a lesser
degree of flexibility than healthy ones)
- age (pre-adolescents are generally more flexible than adults)
- gender (females are generally more flexible than males)
- one's ability to perform a particular exercise (practice makes
perfect)
- one's commitment to achieving flexibility
- the restrictions of any clothing or equipment
Some sources also the suggest that water is an important dietary element
with regard to flexibility. Increased water intake is believed to
contribute to increased mobility, as well as increased total body
relaxation.
Rather than discuss each of these factors in significant detail as
Gummerson does, I will attempt to focus on some of the more common factors
which limit one's flexibility. According to `SynerStretch', the most
common factors are: bone structure, muscle mass, excess fatty tissue, and
connective tissue (and, of course, physical injury or disability).
Depending on the type of joint involved and its present condition (is it
healthy?), the bone structure of a particular joint places very noticeable
limits on flexibility. This is a common way in which age can be a factor
limiting flexibility since older joints tend not to be as healthy as
younger ones.
Muscle mass can be a factor when the muscle is so heavily developed that it
interferes with the ability to take the adjacent joints through their
complete range of motion (for example, large hamstrings limit the ability
to fully bend the knees). Excess fatty tissue imposes a similar restriction.
The majority of "flexibility" work should involve performing exercises
designed to reduce the internal resistance offered by soft connective
tissues (See "1.3 - Connective Tissue"). Most stretching exercises attempt
to accomplish this goal and can be performed by almost anyone, regardless
of age or gender.
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Subject: 2.2.1 - How Connective Tissue Affects Flexibility
The resistance to lengthening that is offered by a muscle is dependent upon
its connective tissues: When the muscle elongates, the surrounding
connective tissues become more taut (See "1.3 - Connective Tissue"). Also,
inactivity of certain muscles or joints can cause chemical changes in
connective tissue which restrict flexibility. To quote M. Alter directly:
A question of great interest to all athletes is the relative importance
of various tissues in joint stiffness. The joint capsule (i.e., the
saclike structure that encloses the ends of bones) and ligaments are
the most important factors, accounting for 47 percent of the stiffness,
followed by the muscle's fascia (41 percent), the tendons (10 percent),
and skin (2 percent). However, most efforts to increase flexibility
through stretching should be directed to the muscle fascia. The
reasons for this are twofold. First, muscle and its fascia have more
elastic tissue, so they are more modifiable in terms of reducing
resistance to elongation. Second, because ligaments and tendons have
less elasticity than fascia, it is undesirable to produce too much
slack in them. Overstretching these structures may weaken the
integrity of joints. As a result, an excessive amount of flexibility
may destabilize the joints and *increase* an athlete's risk of injury.
When connective tissue is overused, the tissue becomes fatigued and may
tear, which also limits flexibility. When connective tissue is unused or
under used, it provides significant resistance and limits flexibility. The
elastin begins to fray and loses some of its elasticity, and the collagen
increases in stiffness and in density. Aging has some of the same effects
on connective tissue that lack of use has.
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Subject: 2.2.2 - How Aging Affects Flexibility
With appropriate training, flexibility can, and should, be developed at all
ages. This does not imply, however, that flexibility can be developed at
the same rate by everyone. In general, the older you are, the longer it
will take to develop the desired level of flexibility. Hopefully, you'll be
more patient if you're older.
According to M. Alter, the main reason we become less flexible as we get
older is a result of certain changes that take place in our connective
tissues:
The primary factor responsible for the decline of flexibility with age
is certain changes that occur in the connective tissues of the body.
Interestingly, it has been suggested that exercise can delay the loss
of flexibility due to the aging process of dehydration. This is based
on the notion that stretching stimulates the production or retention of
lubricants between the connective tissue fibers, thus preventing the
formation of adhesions.
M. Alter further states that some of the physical changes attributed to
aging are the following:
* An increased amount of calcium deposits, adhesions, and cross-links in
the body
* An increase in the level of fragmentation and dehydration
* Changes in the chemical structure of the tissues.
* Loss of "suppleness" due to the replacement of muscle fibers with
fatty, collagenous fibers.
This does *not* mean that you should give up trying to achieve flexibility
if you are old or inflexible. It just means that you need to work harder,
and more carefully, for a longer period of time when attempting to increase
flexibility. Increases in the ability of muscle tissues and connective
tissues to elongate (stretch) can be achieved at any age.
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Subject: 2.3 - Strength and Flexibility
Strength training and flexibility training should go hand in hand. It is a
common misconception that there must always be a trade-off between
flexibility and strength. Obviously, if you neglect flexibility training
altogether in order to train for strength then you are certainly
sacrificing flexibility (and vice versa). However, performing exercises
for both strength and flexibility need not sacrifice either one. As a
matter of fact, flexibility training and strength training can actually
enhance one another.
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Subject: 2.3.1 - Why Bodybuilders Should Stretch
One of the best times to stretch is right after a strength workout such as
weightlifting. Static stretching of fatigued muscles (See "3.5 - Static
Stretching") performed immediately following the exercise(s) that caused
the fatigue, helps not only to increase flexibility, but also enhances the
promotion of muscular development (muscle growth), and will actually help
decrease the level of post-exercise soreness. Here's why:
After you have used weights (or other means) to overload and fatigue your
muscles, your muscles retain a "pump" and are shortened somewhat. This
"shortening" is due mostly to the repetition of intense muscle activity
that often only takes the muscle through part of its full range of motion.
This "pump" makes the muscle appear bigger. The "pumped" muscle is also
full of lactic acid and other by-products from exhaustive exercise. If the
muscle is not stretched afterward, it will retain this decreased range of
motion (it sort of "forgets" how to make itself as long as it could) and
the buildup of lactic acid will cause post-exercise soreness. Static
stretching of the "pumped" muscle helps it to become "looser", and to
"remember" its full range of movement. It also helps to remove lactic acid
and other waste-products from the muscle. While it is true that stretching
the "pumped" muscle will make it appear visibly smaller, it does not
decrease the muscle's size or inhibit muscle growth. It merely reduces the
"tightness" (contraction) of the muscles so that they do not "bulge" as
much.
Also, strenuous workouts will often cause damage to the muscle's connective
tissue. The tissue heals in 1 to 2 days but it is believed that the tissues
heal at a shorter length (decreasing muscular development as well as
flexibility). To prevent the tissues from healing at a shorter length,
physiologists recommend static stretching after strength workouts.
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Subject: 2.3.2 - Why Contortionists Should Strengthen
You should be "tempering" (or balancing) your flexibility training with
strength training (and vice versa). Do not perform stretching exercises for
a given muscle group without also performing strength exercises for that
same group of muscles. Judy Alter, in her book `Stretch and Strengthen',
recommends stretching muscles after performing strength exercises, and
performing strength exercises for every muscle you stretch. In other words:
"Strengthen what you stretch, and stretch after you strengthen!"
The reason for this is that flexibility training on a regular basis causes
connective tissues to stretch which in turn causes them to loosen (become
less taut) and elongate. When the connective tissue of a muscle is weak, it
is more likely to become damaged due to overstretching, or sudden, powerful
muscular contractions. The likelihood of such injury can be prevented by
strengthening the muscles bound by the connective tissue. Kurz suggests
dynamic strength training consisting of light dynamic exercises with
weights (lots of reps, not too much weight), and isometric tension
exercises. If you also lift weights, dynamic strength training for a
muscle should occur *before* subjecting that muscle to an intense
weightlifting workout. This helps to pre-exhaust the muscle first, making
it easier (and faster) to achieve the desired overload in an intense
strength workout. Attempting to perform dynamic strength training *after*
an intense weightlifting workout would be largely ineffective.
If you are working on increasing (or maintaining) flexibility then it is
*very* important that your strength exercises force your muscles to take
the joints through their full range of motion. According to Kurz:
Repeating movements that do not use a full range of motion in the
joints (e.g., bicycling, certain techniques of Olympic weightlifting,
pushups) can cause a shortening of the muscles surrounding the joints
of the working limbs. This shortening is a result of setting the
nervous control of length and tension in the muscles at the values
repeated most often or most strongly. Stronger stimuli are remembered
better.
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Subject: 2.4 - Overflexibility
It is possible for the muscles of a joint to become too flexible.
According to `SynerStretch':
There is a tradeoff between flexibility and stability. The looser you
get, the less support offered to the joints by their adjacent muscles.
Excessive flexibility can be just as much of a liability as not enough
flexibility. Either one increases your risk of injury.
Once a muscle has reached its absolute maximum length, attempting to
stretch the muscle further only serves to stretch the ligaments and put
undue stress upon the tendons (two things that you do *not* want to
stretch). Ligaments will tear when stretched more than 6% of their normal
length. Tendons are not even supposed to be able to lengthen. Even when
stretched ligaments and tendons do not tear, loose joints and/or a decrease
in the joint's stability can occur (thus vastly increasing your risk of
injury).
Once you have achieved the desired level of flexibility for a muscle or set
of muscles and have maintained that level for a solid week, you should
discontinue any isometric or PNF stretching of that muscle until some of
its flexibility is lost (See "3.6 - Isometric Stretching"), and See "3.7 -
PNF Stretching").
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Subject: 3 - Types of Stretching
Just as there are different types of flexibility, there are also different
types of stretching. Stretches are either dynamic (meaning they involve
motion) or static (meaning they involve no motion). Dynamic stretches
affect dynamic flexibility and static stretches affect static flexibility
(and dynamic flexibility to some degree).
The different types of stretching are:
1. ballistic stretching
2. dynamic stretching
3. active stretching
4. passive (or relaxed) stretching
5. static stretching
6. isometric stretching
7. PNF stretching
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Subject: 3.1 - Ballistic Stretching
Ballistic stretching uses the momentum of a moving body or a limb in an
attempt to force it beyond its normal range of motion. This is stretching,
or "warming up", by bouncing into (or out of) a stretched position, using
the stretched muscles as a spring which pulls you out of the stretched
position. (e.g. bouncing down repeatedly to touch your toes.) This type
of stretching is not considered useful and can lead to injury. It does not
allow your muscles to adjust to, and relax in, the stretched position. It
may instead cause them to tighten up by repeatedly activating the stretch
reflex (See "1.6.2 - The Stretch Reflex").
------------------------------
Subject: 3.2 - Dynamic Stretching
"Dynamic stretching", according to Kurz, "involves moving parts of your
body and gradually increasing reach, speed of movement, or both." Do not
confuse dynamic stretching with ballistic stretching! Dynamic stretching
consists of controlled leg and arm swings that take you (gently!) to the
limits of your range of motion. Ballistic stretches involve trying to
force a part of the body *beyond* its range of motion. In dynamic
stretches, there are no bounces or "jerky" movements. An example of
dynamic stretching would be slow, controlled leg swings, arm swings, or
torso twists.
Dynamic stretching improves dynamic flexibility and is quite useful as part
of your warm-up for an active or aerobic workout (such as a dance or
martial-arts class). (See "4.1 - Warming Up").
According to Kurz, dynamic stretching exercises should be performed in sets
of 8-12 repetitions:
Perform your exercises (leg raises, arm swings) in sets of eight to
twelve repetitions. If after a few sets you feel tired - stop. Tired
muscles are less elastic, which causes a decrease in the amplitude of
your movements. Do only the number of repetitions that you can do
without decreasing your range of motion. More repetitions will only set
the nervous regulation of the muscles' length at the level of these
less than best repetitions and may cause you to lose some of your
flexibility. What you repeat more times or with a greater effort will
leave a deeper trace in your [kinesthetic] memory! After reaching the
maximal range of motion in a joint in any direction of movement, you
should not do many more repetitions of this movement in a given
workout. Even if you can maintain a maximal range of motion over many
repetitions, you will set an unnecessarily solid memory of the range of
these movements. You will then have to overcome these memories in order
to make further progress.
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Subject: 3.3 - Active Stretching
"Active stretching" is also referred to as "static-active stretching". An
active stretch is one where you assume a position and then hold it there
with no assistance other than using the strength of your agonist muscles
(See "1.4 - Cooperating Muscle Groups"). For example, bringing your leg up
high and then holding it there without anything (other than your leg
muscles themselves) to keep the leg in that extended position. The tension
of the agonists in an active stretch helps to relax the muscles being
stretched (the antagonists) by reciprocal inhibition (See "1.6.4 -
Reciprocal Inhibition").
Active stretching increases active flexibility and strengthens the
agonistic muscles. Active stretches are usually quite difficult to hold and
maintain for more than 10 seconds and rarely need to be held any longer
than 15 seconds.
Many of the movements (or stretches) found in various forms of yoga are
active stretches.
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Subject: 3.4 - Passive Stretching
"Passive stretching" is also referred to as "relaxed stretching", and as
"static-passive stretching". A passive stretch is one where you assume a
position and hold it with some other part of your body, or with the
assistance of a partner or some other apparatus. For example, bringing your
leg up high and then holding it there with your hand. The splits is an
example of a passive stretch (in this case the floor is the "apparatus"
that you use to maintain your extended position).
Slow, relaxed stretching is useful in relieving spasms in muscles that are
healing after an injury. Obviously, you should check with your doctor first
to see if it is okay to attempt to stretch the injured muscles (See "4.12 -
Pain and Discomfort").
Relaxed stretching is also very good for "cooling down" after a workout and
helps reduce post-workout muscle fatigue, and soreness. (See "4.2 -
Cooling Down").
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Subject: 3.5 - Static Stretching
Many people use the term "passive stretching" and "static stretching"
interchangeably. However, there are a number of people who make a
distinction between the two. According to M. Alter:
"Static stretching" involves holding a position. That is, you stretch
to the farthest point and hold the stretch ...
"Passive stretching" is a technique in which you are relaxed and make
no contribution to the range of motion. Instead, an external force is
created by an outside agent, either manually or mechanically.
Notice that the definition of passive stretching given in the previous
section encompasses *both* of the above definitions. Throughout this
document, when the term "static stretching" or "passive stretching" is
used, its intended meaning is the definition of passive stretching as
described in the previous section. You should be aware of these alternative
meanings, however, when looking at other references on stretching.
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Subject: 3.6 - Isometric Stretching
"Isometric stretching" is a type of static stretching (meaning it does not
use motion) which involves the resistance of muscle groups through
isometric contractions (tensing) of the stretched muscles (See "1.5 - Types
of Muscle Contractions"). The use of isometric stretching is one of the
fastest ways to develop increased static-passive flexibility and is much
more effective than either passive stretching or active stretching alone.
Isometric stretches also help to develop strength in the "tensed" muscles
(which helps to develop static-active flexibility), and seems to decrease
the amount of pain usually associated with stretching.
The most common ways to provide the needed resistance for an isometric
stretch are to apply resistance manually to one's own limbs, to have a
partner apply the resistance, or to use an apparatus such as a wall (or the
floor) to provide resistance.
An example of manual resistance would be holding onto the ball of your foot
to keep it from flexing while you are using the muscles of your calf to try
and straighten your instep so that the toes are pointed.
An example of using a partner to provide resistance would be having a
partner hold your leg up high (and keep it there) while you attempt to
force your leg back down to the ground.
An example of using the wall to provide resistance would be the well known
"push-the-wall" calf-stretch where you are actively attempting to move the
wall (even though you know you can't).
Isometric stretching is *not* recommended for children and adolescents
whose bones are still growing. These people are usually already flexible
enough that the strong stretches produced by the isometric contraction have
a much higher risk of damaging tendons and connective tissue. Kurz
strongly recommends preceding any isometric stretch of a muscle with
dynamic strength training for the muscle to be stretched. A full session of
isometric stretching makes a lot of demands on the muscles being stretched
and should not be performed more than once per day for a given group of
muscles (ideally, no more than once every 36 hours).
The proper way to perform an isometric stretch is as follows:
1. Assume the position of a passive stretch for the desired muscle.
2. Next, tense the stretched muscle for 7-15 seconds (resisting against
some force that will not move, like the floor or a partner).
3. Finally, relax the muscle for at least 20 seconds.
Some people seem to recommend holding the isometric contraction for longer
than 15 seconds, but according to `SynerStretch' (the videotape), research
has shown that this is not necessary. So you might as well make your
stretching routine less time consuming.
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Subject: 3.6.1 - How Isometric Stretching Works
Recall from our previous discussion (See "1.2.1 - How Muscles Contract")
that there is no such thing as a partially contracted muscle fiber: when a
muscle is contracted, some of the fibers contract and some remain at rest
(more fibers are recruited as the load on the muscle increases).
Similarly, when a muscle is stretched, some of the fibers are elongated and
some remain at rest (See "1.6 - What Happens When You Stretch"). During an
isometric contraction, some of the resting fibers are being pulled upon
from both ends by the muscles that are contracting. The result is that some
of those resting fibers stretch!
Normally, the handful of fibers that stretch during an isometric
contraction are not very significant. The true effectiveness of the
isometric contraction occurs when a muscle that is already in a stretched
position is subjected to an isometric contraction. In this case, some of
the muscle fibers are already stretched before the contraction, and, if
held long enough, the initial passive stretch overcomes the stretch reflex
(See "1.6.2 - The Stretch Reflex") and triggers the lengthening reaction
(See "1.6.3 - The Lengthening Reaction"), inhibiting the stretched fibers
from contracting. At this point, according to `SynerStretch':
When you isometrically contracted, some of the resting fibers would
contract, many of the resting fibers would stretch, and many of the
already stretched fibers, which are being prevented from contracting by
the inverse myotatic reflex [the lengthening reaction], would stretch
even more. When the isometric contraction was relaxed and the
contracting fibers returned to their resting length, the stretched
fibers would retain their ability to stretch beyond their normal limit.
... the whole muscle would be able to stretch beyond its initial
maximum, and you would have increased flexibility ...
The reason that the stretched fibers develop and retain the ability to
stretch beyond their normal limit during an isometric stretch has to do
with the muscle spindles (See "1.6.1 - Proprioceptors"): The signal which
tells the muscle to contract voluntarily, also tells the muscle spindle's
(intrafusal) muscle fibers to shorten, increasing sensitivity of the
stretch reflex. This mechanism normally maintains the sensitivity of the
muscle spindle as the muscle shortens during contraction. This allows the
muscle spindles to habituate (become accustomed) to an even
further-lengthened position.
------------------------------
Subject: 3.7 - PNF Stretching
PNF stretching is currently the fastest and most effective way known to
increase static-passive flexibility. PNF is an acronym for "proprioceptive
neuromuscular facilitation". It is not really a type of stretching but is
a technique of combining passive stretching (See "3.4 - Passive
Stretching") and isometric stretching (See "3.6 - Isometric Stretching") in
order to achieve maximum static flexibility. Actually, the term PNF
stretching is itself a misnomer. PNF was initially developed as a method
of rehabilitating stroke victims. PNF refers to any of several
"post-isometric relaxation" stretching techniques in which a muscle group
is passively stretched, then contracts isometrically against resistance
while in the stretched position, and then is passively stretched again
through the resulting increased range of motion. PNF stretching usually
employs the use of a partner to provide resistance against the isometric
contraction and then later to passively take the joint through its
increased range of motion. It may be performed, however, without a
partner, although it is usually more effective with a partner's assistance.
Most PNF stretching techniques employ "isometric agonist
contraction/relaxation" where the stretched muscles are contracted
isometrically and then relaxed. Some PNF techniques also employ "isometric
antagonist contraction" where the antagonists of the stretched muscles are
contracted. In all cases, it is important to note that the stretched muscle
should be rested (and relaxed) for at least 20 seconds before performing
another PNF technique. The most common PNF stretching techniques are:
the "hold-relax"
This technique is also called the "contract-relax". After assuming an
initial passive stretch, the muscle being stretched is isometrically
contracted for 7-15 seconds, after which the muscle is briefly relaxed
for 2-3 seconds, and then immediately subjected to a passive stretch
which stretches the muscle even further than the initial passive
stretch. This final passive stretch is held for 10-15 seconds. The
muscle is then relaxed for 20 seconds before performing another PNF
technique.
the "hold-relax-contract"
This technique is also called the "contract-relax-contract", and the
"contract-relax-antagonist-contract" (or "CRAC"). It involves
performing two isometric contractions: first of the agonists, then, of
the antagonists. The first part is similar to the hold-relax where,
after assuming an initial passive stretch, the stretched muscle is
isometrically contracted for 7-15 seconds. Then the muscle is relaxed
while its antagonist immediately performs an isometric contraction that
is held for 7-15 seconds. The muscles are then relaxed for 20 seconds
before performing another PNF technique.
the "hold-relax-swing"
This technique (and a similar technique called the "hold-relax-bounce")
actually involves the use of dynamic or ballistic stretches in
conjunction with static and isometric stretches. It is *very* risky,
and is successfully used only by the most advanced of athletes and
dancers that have managed to achieve a high level of control over
their muscle stretch reflex (See "1.6.2 - The Stretch Reflex"). It is
similar to the hold-relax technique except that a dynamic or ballistic
stretch is employed in place of the final passive stretch.
Notice that in the hold-relax-contract, there is no final passive stretch.
It is replaced by the antagonist-contraction which, via reciprocal
inhibition (See "1.6.4 - Reciprocal Inhibition"), serves to relax and
further stretch the muscle that was subjected to the initial passive
stretch. Because there is no final passive stretch, this PNF technique is
considered one of the safest PNF techniques to perform (it is less likely
to result in torn muscle tissue). Some people like to make the technique
even more intense by adding the final passive stretch after the second
isometric contraction. Although this can result in greater flexibility
gains, it also increases the likelihood of injury.
Even more risky are dynamic and ballistic PNF stretching techniques like
the hold-relax-swing, and the hold-relax-bounce. If you are not a
professional athlete or dancer, you probably have no business attempting
either of these techniques (the likelihood of injury is just too great).
Even professionals should not attempt these techniques without the guidance
of a professional coach or training advisor. These two techniques have the
greatest potential for rapid flexibility gains, but only when performed by
people who have a sufficiently high level of control of the stretch reflex
in the muscles that are being stretched.
Like isometric stretching (See "3.6 - Isometric Stretching"), PNF
stretching is also not recommended for children and people whose bones are
still growing (for the same reasons. Also like isometric stretching, PNF
stretching helps strengthen the muscles that are contracted and therefore
is good for increasing active flexibility as well as passive flexibility.
Furthermore, as with isometric stretching, PNF stretching is very strenuous
and should be performed for a given muscle group no more than once per day
(ideally, no more than once per 36 hour period).
The initial recommended procedure for PNF stretching is to perform the
desired PNF technique 3-5 times for a given muscle group (resting 20
seconds between each repetition). However, `HFLTA' cites a 1987 study
whose results suggest that performing 3-5 repetitions of a PNF technique
for a given muscle group is not necessarily any more effective than
performing the technique only once. As a result, in order to decrease the
amount of time taken up by your stretching routine (without decreasing its
effectiveness), `HFLTA' recommends performing only one PNF technique per
muscle group stretched in a given stretching session.
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Subject: 3.7.1 - How PNF Stretching Works
Remember that during an isometric stretch, when the muscle performing the
isometric contraction is relaxed, it retains its ability to stretch beyond
its initial maximum length (See "3.6.1 - How Isometric Stretching Works").
Well, PNF tries to take immediate advantage of this increased range of
motion by immediately subjecting the contracted muscle to a passive stretch.
The isometric contraction of the stretched muscle accomplishes several
things:
1. As explained previously (See "3.6.1 - How Isometric Stretching Works"),
it helps to train the stretch receptors of the muscle spindle to
immediately accommodate a greater muscle length.
2. The intense muscle contraction, and the fact that it is maintained for
a period of time, serves to fatigue many of the fast-twitch fibers of
the contracting muscles (See "1.2.2 - Fast and Slow Muscle Fibers").
This makes it harder for the fatigued muscle fibers to contract in
resistance to a subsequent stretch (See "1.6.2 - The Stretch Reflex").
3. The tension generated by the contraction activates the golgi tendon
organ (See "1.6.1 - Proprioceptors"), which inhibits contraction of
the muscle via the lengthening reaction (See "1.6.3 - The Lengthening
Reaction"). Voluntary contraction during a stretch increases tension
on the muscle, activating the golgi tendon organs more than the
stretch alone. So, when the voluntary contraction is stopped, the
muscle is even more inhibited from contracting against a subsequent
stretch.
PNF stretching techniques take advantage of the sudden "vulnerability" of
the muscle and its increased range of motion by using the period of time
immediately following the isometric contraction to train the stretch
receptors to get used to this new, increased, range of muscle length. This
is what the final passive (or in some cases, dynamic) stretch accomplishes.
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Brad_Appleton@ivhs.mot.com Motorola PNSB, Northbrook, IL USA
"And miles to go before I sleep." DISCLAIMER: I said it, not my employer!