In the case of Special Warfare Operators, flexibility refers to the optimum range of
motion surrounding a particular joint that is necessary for peak performance. Range ofmotion is specific to each joint and dependent upon:
- Joint surfaces and capsule and the degree of movement required for the joint to function.
- Muscles, tendons, ligaments and connective tissue associated with limb movement around a joint
There are two types of flexibility:dynamic and static.
Dynamic or active flexibility refers to the speed attained within a range of motion
at the joint during physical performance. This type of flexibility involves the intrinsic
musculature surrounding the joint and its ability to overcome resistance to motion. An
example would be the flexibility required to throw a baseball, punch a boxing opponent, or
perform a martial arts kick. Static or passive flexibility refers to the maximal range of
motion of a joint during passive movement induced by an external source (e.g., a partner,
equipment, gravity). The range of static flexibility is always greater than that of dynamic
flexibility.
The Stretch Reflex and the Lengthening Reaction
The stretch reflex and the lengthening reaction are joint-protective mechanisms in
which sensory organs, located in the muscles and tendons surrounding a joint, are activated
when muscles are stretched. As seen in Figure 7-1, the two sensory organs involved in
monitoring muscle tightness are the muscle spindle cells and golgi tendon organs (GTOs).
The stretch reflex involves muscle spindles which lie parallel to the muscle fiber.
These spindles are very sensitive to changes in muscle length. When the muscle stretches,
muscle spindles send signals to the spinal cord, which in turn, sends signals to the muscle
telling it to contract in order to protect the muscle from potential tissue damage. The classic
example of the stretch reflex occurs when a physician taps a patient just below the kneecap.
The quadriceps muscle is quickly stretched, and the muscle spindles react by contracting
the quadriceps muscle causing the knee-jerk response. The greater or more rapid the
stretch, the greater the response of the muscle spindles and the resultant muscle contraction.
Signals are high in frequency at the beginning of a stretch, but then slow down as they adapt
to the new length.
The lengthening reaction engages GTOs, which are located in the muscle-tendon
junctions, and activates them when the tension in a tendon is increased as a result of either
muscular contraction, stretching the muscle beyond its resting length, or a combination of
the two. When muscular tension increases, the GTOs respond by sending inhibitory signals
to the muscle; this causes the muscles to relax, and protects the muscles and tendons from
tearing due to tension overload. Knowledge of the stretch reflex and the lengthening
reaction is useful for effective stretching.
The most effective stretches are performed
slowly, and held for 15 - 30 seconds.
Performing the stretch slowly avoids excessive activation of the muscle spindles
and resultant muscular contraction. Holding the stretch allows time for the muscle spindles
to adapt to the new muscle length, and eventually, to achieve greater lengths. The length
and duration of the stretch should also be sufficient to activate the GTOs so that they
override the muscle spindles and induce muscular relaxation.