3.7.1 - How PNF Stretching Works
Description
This article is from the Stretching FAQ, by Brad Appleton Brad_Appleton@ivhs.mot.com with numerous contributions by others.
3.7.1 - How PNF Stretching Works
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 (See "3.6.1 - How Isometric Stretching Works").
Well, 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:
1. As explained previously (See "3.6.1 - How Isometric Stretching Works"),
it helps to train the stretch receptors of the muscle spindle to
immediately accommodate a greater muscle length.
2. 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 (See "1.2.2 - Fast and Slow Muscle Fibers").
This makes it harder for the fatigued muscle fibers to contract in
resistance to a subsequent stretch (See "1.6.2 - The Stretch Reflex").
3. The tension generated by the contraction activates the golgi tendon
organ (See "1.6.1 - Proprioceptors"), which inhibits contraction of
the muscle via the lengthening reaction (See "1.6.3 - 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.
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