The Navy SEAL Physical Fitness Guide - Uniformed Services ...

above, when a muscle is slowly stretched and held, the resulting tension triggers thelengthening reaction which prevents the stretched muscle fibers from contracting. Whenthis stretched muscle is then isometrically contracted, the following happens:" During an isometric contraction, some fibers will contract, but others willstretch even further. When the contraction is stopped, the contracted fibersreturn to their starting position, while the stretched fibers retain theirstretched position (due to muscle spindle accommodation) and are able tolengthen even further." The increased tension within the muscles generated by an isometric contractionactivates the GTO which triggers the lengthening reaction, and inhibitsfurther contraction. When the isometric contraction is stopped, the muscle isstill inhibited from further contraction and able to lengthen further.The final stretch, which follows isometric contraction, takes advantage of themuscle's ability to elongate further, and allows the muscle, tendon, and sense organs toadapt to greater lengths.It is best to have a partner help whenusing PNF techniques.A common PNF technique is referred to as the “contract-relax method”.Instructions for and a pictorial representation of this method are provided in Figure 7-2.This technique uses passive stretch and isometric contractions, followed by musclerelaxation and passive stretching to the new range of motion. For example, if you arestretching your hamstrings, you first passively take the stretch to the point of tightness andhold. Then you isometrically contract the hamstrings by using this muscle to apply forceagainst an object or partner (See Figure 7-2). Following the contraction, the muscle isallowed to relax and the muscle is then passively stretched and held. Currentrecommendations suggest performing this technique with one to five repetitions, but likeweight training, it needs to be done no more than three to five times a week.114 Flexibility