Proprioceptive Neuromuscular Facilitation
Proprioceptive Neuromuscular Facilitation (PNF) is a more advanced form of flexibility training that involves both the stretching and contraction of the muscle group being targeted. PNF stretching was originally developed as a form of rehabilitation, and 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, then passively stretched again through the resulting increased range of motion. It is also excellent for targeting specific muscle groups, and as well as increasing flexibility and muscular strength.
How to Perform a PNF Stretch
The muscle group is relaxed, then immediately and cautiously pushed past its normal range of movement for about 20 to 30 seconds. Allow 30 seconds recovery before repeating the procedure 2 - 4 times. The athlete and partner assume the position for the stretch, and then the partner extends the body limb until the muscle is stretched and tension is felt. The athlete then contracts the stretched muscle for 5 - 6 seconds and the partner must inhibit all movement. (The force of the contraction should be relevant to the condition of the muscle. For example, if the muscle has been injured, do not apply a maximum contraction). The muscle group is relaxed, then immediately and cautiously pushed past its normal range of movement for about 20 to 30 seconds. Allow 30 seconds recovery before repeating the procedure 2 - 4 times.
Other common PNF stretching techniques are:
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.
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.
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. This is a technique that is most commonly used by the advanced of athletes with a high level of control over their muscle 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.
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. 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:
It helps to train the stretch receptors of the muscle spindle to immediately accommodate a greater muscle length.
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. This makes it harder for the fatigued muscle fibers to contract in resistance to a subsequent stretch.
The tension generated by the contraction activates the golgi tendon organ, which inhibits contraction of the muscle via 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.