Traditional static stretching exercises are no longer considered the best way to increase joint mobility in most rehabilitative programs. Muscles and connective tissues require both time and frequency in order to change length through the process of soft-tissue "creep." Creep refers to the ability of a tissue to elongate over time when a constant load is applied to it.
A more intensive stretching routine often must be provided by the treating doctor in order to increase flexibility. A good example is the use of a specific proprioceptive neuromuscular facilitation (PNF) technique known as "contract-relax, antagonist contract" (CRAC).1
Stretching for Flexibility
Stretching refers to tissue elongation - extending a material or substance from its resting length. This occurs as a continuum, so stretches can range from a minimal length to a maximum length. Flexibility describes the range of movement (ROM) possible around a joint. This varies considerably from one individual to the next and is dependent on several types of tissues.
What Tissues Are Elongated?
Muscle. Skeletal muscle has elastic properties similar to those of a rubber band: It can lengthen and return to a resting state. The length of a muscle cannot be increased by nervous impulse; therefore, an external force must be applied. Such external forces include gravity, momentum, an antagonist muscle group contracting, or application of an external force, such as a weight or using a partner or assistant.
Connective tissue. This refers primarily to fascia, which covers each muscle fiber and forms the compartment that surrounds each muscle. Fascia, particularly that which forms the muscle compartment, can provide a great deal of resistance to stretching. It has viscoelastic properties similar to the properties of both plasticine and rubber. Like plasticine, the viscous components when stretched will remain in the new position. The elastic components, like a stretched rubber band, will return to a resting length after stretching. Therefore, it is possible for fascia, with its plastic component, to change its length permanently - a vital consideration for long-held stretches.
Ligaments and tendons.
Ligaments and tendons often are inadvertently stretched when muscles are used or stretched. However, the deliberate stretching of these tissues may result in excessive mobility of joints, which can decrease the local stability.
Specialized nerve endings.
Muscle spindles (the stretch reflex) are located within muscles, and they detect the rate and length of stretch on a muscle. If the stretch is too fast or too far, these nerve endings stimulate the muscle to contract to protect itself from overstretching.
Golgi tendon organs (inverse stretch reflex) are nerve endings located in tendons. They are slower to respond to increased stretch or tension in the muscle. This is also a protective mechanism. When a great degree of tension is experienced, either through contracting or stretching the muscle, the Golgi tendon causes the muscle to relax to avoid possible rupturing.
Contract-Relax Stretching
This basic stretching technique takes advantage of the neuromuscular inhibition that occurs following a muscular contraction.2 The first step involves passively lengthening the muscle to be stretched to its end of range. At its point of full length, the patient then gently contracts this muscle against resistance (usually another person), which limits movement. This isometric contraction is continued at about 50 percent of maximal effort for at least six seconds (which allows autogenic inhibition to occur). The muscle is then relaxed, taken to a new range and held for about 20 seconds. This can be repeated three to four times.
CRAC Procedure
An extra step can now be added which makes the stretching process more effective. The first part of this stretch is similar to the contract-relax method above; however, when the muscle to be stretched is relaxed after its six-second contraction, the opposite or antagonist muscle is contracted for at least six seconds (allowing reciprocal inhibition to occur). The antagonist is then relaxed and the stretched muscle is taken to a new range. This process can be repeated several times to establish a new resting length of the tissues, and a new set point for the stretch receptors.3
Stretching is a vital component of treatment for many musculoskeletal problems. Applying the CRAC approach can make stretching considerably more effective.
References
- Surburg P, Schrader J. Proprioceptive neuromuscular facilitation techniques in sports medicine: a reassessment. J Athletic Training 1997;11:34-39.
- Burke D, Culligan C, Holt L. The theoretical basis of proprioceptive neuromuscular facilitation. J Strength Cond Res 2000;14:496-500.
- Carter A, Kinzey S, Chitwood L, Cole J. Proprioceptive neuromuscular facilitation decreases muscle activity during the stretch reflex in selected posterior thigh muscles. J Sports Rehabil 2000;9:269-278.
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