114 Flexibility
above, when a muscle is slowly stretched and held, the resulting tension triggers the
lengthening reaction which prevents the stretched muscle fibers from contracting. When
this stretched muscle is then isometrically contracted, the following happens:" During an isometric contraction, some fibers will contract, but others will
stretch even further. When the contraction is stopped, the contracted fibers
return to their starting position, while the stretched fibers retain their
stretched position (due to muscle spindle accommodation) and are able to
lengthen even further." The increased tension within the muscles generated by an isometric contrac-
tion activates the GTO which triggers the lengthening reaction, and inhibits
further contraction. When the isometric contraction is stopped, the muscle is
still inhibited from further contraction and able to lengthen further.The final stretch, which follows isometric contraction, takes advantage of the
muscle's ability to elongate further, and allows the muscle, tendon, and sense organs to
adapt to greater lengths.It is best to have a partner help when
using 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 muscle
relaxation and passive stretching to the new range of motion. For example, if you are
stretching your hamstrings, you first passively take the stretch to the point of tightness and
hold. Then you isometrically contract the hamstrings by using this muscle to apply force
against an object or partner (See Figure 7-2). Following the contraction, the muscle is
allowed to relax and the muscle is then passively stretched and held. Current
recommendations suggest performing this technique with one to five repetitions, but like
weight training, it needs to be done no more than three to five times a week.