Walshe, A. D., Wilson, G. J., & Ettema, G. J. (1998). Stretch-shorten cycle compared with isometric pre-load: Contributions to enhanced muscular performance. Journal of Applied Physiology, 84, 97-106.

Trained males (N = 40) performed squats under three different preparatory phase (usually the eccentric contraction phase) conditions; a) no preparation (concentric-only (CO) squat), b) isometric pre-load (IS), and c) stretch-shorten (SS - normal).

Work output was significantly greater for both IS and SS conditions when compared to the CO condition over the first 300 ms. It was concluded that the preparatory phase activity of a squat influenced the actual squat because it produced a higher level of muscle activity from which the concentric phase would be initiated.

Implication. The preparatory phase of a two-phase motor action will influence concentric phase activity. The higher the level of activity in the preparatory phase, the better will be the overall performance. When developing power activities, an emphasis on the preparatory phase, usually the eccentric phase of the action, is as important as the release/concentric movement phase.

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