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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)."
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 section Cooperating Muscle Groups). For example, lifting the leg and
keeping it high without any external support (other than from your own
- 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.
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
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
The majority of "flexibility" work should involve performing exercises
designed to reduce the internal resistance offered by soft connective
tissues (see section Connective Tissue). Most stretching exercises attempt
to accomplish this goal and can be performed by almost anyone,
regardless of age or gender.
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 section Connective Tissue). Also,
inactivity of certain muscles or joints can cause chemical changes in
connective tissue which restrict flexibility. According to M.
Alter, each type of tissue plays a certain role 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)".
M. Alter goes on to say that efforts to increase flexibility
should be directed at the muscle's fascia however. This is because
it has the most elastic tissue, and because ligaments and tendons
(since they have less elastic tissue) are not intended to stretched
very much at all. Overstretching them may weaken the joint's integrity
and cause destabilization (which increases the 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
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. As we age, our bodies gradually dehydrate to some
extent. It is believed that "stretching stimulates the production or
retention of lubricants between the connective tissue fibers, thus
preventing the formation of adhesions". Hence, exercise can delay some
of the loss of flexibility that occurs due to the aging process.
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
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
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.
One of the best times to stretch is right after a strength workout such
as weightlifting. Static stretching of fatigued muscles (see section 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
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
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
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 employ a full range of motion in
the joints (like cycling, certain weightlifting techniques, and pushups)
can cause of shortening of the muscles surrounding the joints. This is
because the nervous control of length and tension in the muscles are set
at what is repeated most strongly and/or most frequently.
It is possible for the muscles of a joint to become too flexible.
According to SynerStretch, there is a tradeoff between
flexibility and stability. As you get "looser" or more limber
in a particular joint, less support is given to the joint
by its surrounding muscles. Excessive flexibility can be just
as bad as not enough because both increase 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 section Isometric Stretching, and
see section PNF Stretching).
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