In the previous post (Plyometrics part.1 - the ankle 'bounce' reflex), I presented the bounce reflex (ankle stretch shortening cycle). The bounce reflex stores gravitational energy in the calf muscles and Achilles tendon when the feet strike the ground during walking and running. The bounce reflex is critical for quickness and running efficiency, generally.
Plyometric exercise is designed to enhance the bounce reflex. Examples include skipping and hopping. There is a common belief in sport science that the reflex is a single motor ability and a variety of modalities can be used to develop the reflex, and enhance running skills. A recent study (detailed in the previous post) showed that this is not the case. The reflex operates at multiple levels (amplitudes). Jumping activities, for example, involve a heavier footfall/ longer ground reaction moment and more hip-knee drop than running activities.
The selection of jump height is critical in two ways: 1) training amplitude must match the sport or exercise target, and 2) training expectation must be matched by athlete competency and physical strength.
In the first clip below, it can be clearly observed that there is an upper limit for hurdle height for this young woman to preserve her bounce reflex. The young man in the 2nd clip is much stronger and can safely and effectively use larger ground reaction forces. However, this does not mean higher hurdles, with larger forces, will more strongly translate to all running/ jumping sporting targets.
hurdle plyometrics - upper limit of height as a function of strength
hurdle plyometrics - stronger bodies tolerate greater heights
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