IMPORTANT TERMINOLOGY
Golgi Tendon Organ (GTO) – A mechanoreceptor located near the junction of the muscle and tendon. The GTO is sensitive to increasing tension within the muscle.

Autogenic Inhibition - A reflex muscular relaxation that occurs in the same muscle where the GTO is stimulated.

Reciprocal Inhibition – A reflex muscular relaxation that occurs in the muscle that is opposite the muscle where the GTO is stimulated.

Agonist - The muscle that is contracting to create joint movement.

Antagonist - The muscle that opposes the agonist and is therefore stretched during joint movement.

Isometric Muscle Action – A muscular contraction against a fixed resistance where no joint movement occurs.

Concentric Muscle Action – A muscular contraction that produces joint movement.

Passive Static Stretch - A stretch produced by the coach where the end point is held. The athlete remains relaxed throughout.


SCIENTIFIC FOUNDATION OF PNF
PNF stretching techniques are more effective than simple passive stretching. This success is explained by the effect of PNF stretching on the proprioceptors within muscle and tendon. One of these proprioceptors, the Golgi Tendon Organ (GTO) is sensitive to increasing tension within a muscle. When stimulated, the GTO causes muscular relaxation. If this relaxation occurs in the same muscle experiencing the increased tension, the result is called autogenic inhibition. A coach may take advantage of this natural occurrence by having the athlete contract a muscle immediately before a passive stretch of that same muscle thus producing autogenic inhibition. In this example, the tension produced during the contraction stimulates the GTO causing a reflex relaxation of the same muscle during the subsequent passive stretch.

If relaxation occurs in the muscle opposing the muscle experiencing the increased tension, the result is called reciprocal inhibition. During a passive stretch, reciprocal inhibition can be utilized by simultaneously contracting the muscle opposing the muscle being stretched. The tension in the contracting muscle stimulates the GTO and causes a simultaneous reflex relaxation in the opposite muscle.

PNF STRETCHING TECHNIQUES
When describing PNF stretches, antagonist refers to the muscle that is being stretched and agonist refers to the muscle opposite the antagonist. For example, during elbow flexion the elbow extensors (triceps) will be stretched; they are the antagonist muscle group and the elbow flexors (biceps), which cause the movement, are the agonist muscle group.

During PNF stretches, three specific muscle actions can be used to increase the passive stretch or range of motion. Both isometric and concentric muscle actions of the antagonist are used prior to a passive stretch of the antagonist to bring about autogenic inhibition. The isometric muscle action will be called “hold” and the concentric muscle action will be called “contract.” A concentric muscle action of the agonist is used during a passive stretch of the antagonist to bring about reciprocal inhibition. The concentric muscle action of the agonist will be called “agonist contraction.” Each technique also involves passive static stretches called “relax.”

There are three PNF techniques: 1) hold-relax, 2) hold-relax with agonist contraction, and 3) contract-relax. The PNF techniques should be completed in three phases. To begin each of the three techniques, a passive pre-stretch of 10-second duration is used. The pre-stretch establishes the current flexibility limit. The techniques differ based on the muscle actions used in the second and third phases. These phases determine the name for each of the three techniques. A stretch to improve hamstring flexibility will be used to illustrate these techniques.

Hold-relax - This technique begins with a passive pre-stretch that is held at the point of a tight sensation for 10 seconds (Figure 1). Following the 10 seconds, the athlete is instructed to attempt to extend the hip. The coach resists the movement so that an isometric muscle action occurs and is held for six seconds (Figure 2). Then, the athlete is asked to relax and a passive stretch is performed and held for 30 seconds (Figure 3). The final stretch should achieve a greater range of motion due to autogenic inhibition.

Hold-relax with agonist contraction - During the first two phases, this technique is identical to “hold-relax.” It differs, however, by asking the athlete to provide a concentric action of the agonist in addition to the final 30-second passive stretch (Figure 4). The final stretch should be greater due to both autogenic and reciprocal inhibition.

Contract-relax - This technique also begins with a passive pre-stretch that is held at the point of a tight sensation for 10 seconds (Figure 1). Then, the athlete extends the hip against manual resistance from the coach who allows a concentric muscle action through the full range of motion, rather than keeping the hamstring in an isometric contraction (Figure 5). In the next phase, the athlete relaxes and a passive hip flexion stretch force is applied and held by the coach for 30 seconds (Figure 6). The range of motion should be increased due to autogenic inhibition.

PNF stretching should be used after activity in a controlled environment to increase flexibility. Athletes should try each technique and use those that work best for them. Coaches may apply PNF techniques or supervise athletes as they stretch together.


Figure 1 Figure 2 Figure 3




Figure 4 Figure 5 Figure 6