The Effects of Instability on Countermovement Jump Performance

The effects of instability on countermovement jump performance

Post-activation potentiation (PAP) is a phenomenon whereby the performance of explosive movements (e.g. sprints, jumps) can be enhanced by executing a heavy resistance exercise (activation exercise) immediately prior to the explosive movement (Robbins, 2005).   Two possible physiological mechanisms have been suggested to explain PAP: a) an increased phosphorylation of the myosin regulatory light, which allows more calcium ions to bind with actin and myosin enhancing force production at the structural level (Hamada et al., 2000); or b) an enhancement of the H-reflex, a heightened neuromuscular response elicited by the Group Ia afferent muscle nerves which increases efficiency and rate of the nerve impulses to the muscle (Hodgson et al., 2005).

PAP has been found to increase the rate of force development (RFD), a vital component to activities requiring dynamic muscular contractions (Sale, 2002; Baudry & Duchateau, 2007), thus maximising explosive power for athletic performance (Horarth & Kravitz, 2008). A large number of studies have shown acute performance improvements as a result of a PAP protocol (e.g. Sale, 2002; Robbins, 2005). However most studies employ a heavy resistance activation exercise (e.g. back squats, hang cleans) which are not applicable within a real-world competitive setting (e.g. prior to an athletic competition), nor do they mimic the forces, velocities and joint stability required during explosive/jumping actions. Recently, a collection of scientists have started using drop jumps (DJ), a popular plyometric exercise, as a PAP activation exercise to elicit performance improvements in explosive movements. Drop jumps can be easily performed and could be incorporated by athletes, without practical difficulties, into their warm-up routine prior to competitions. The results so far are encouraging since the two most comprehensive studies which employed drop jumps as a component of...