McArdle, W. D., Katch, F. I., & Katch, V. L. (2004). Exercise physiology (5th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.

"Plyometric exercise overloads a muscle to provide forcible and rapid stretch (eccentric, or stretch phase) immediately before the concentric or shortening phase of action. Like many sports situations, the rapid lengthening phase in the stretch-shortening cycle produces a more powerful subsequent movement largely because of two main factors: . . .

• Attainment of a higher active muscle state (greater potential energy) before the concentric shortening action.
• Stretch induced evoking of segmental reflexes that potentiate subsequent muscle activation" (McArdle, Katch, & Katch, pp. 525).

Implication. A baseball pitch involves a plyometric action. When the arm is cocked through very rapid pre-stretch, the muscles' and connective tissues' natural elastic recoil functions are activated, not metabolic muscle shortening.

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