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Figure 4. Multiple jump (15J) height and Power developed by the 4 groups (Means values ± SD). (b) values for GK significantly higher than for MF (P<0.05). (bb) values for GK significantly higher than for MF (P<0.01). (c) values for GK significantly higher than for FW (P<0.05). (cc) values for GK significantly higher than for FW (P<0.01). (e) values for DF significantly higher than for MF (P<0.05). (ee) values for DF significantly higher than for MF (P<0.01). (f) values for DF significantly higher than for FW (P<0.05). (ff) values for DF significantly higher than for FW (P<0.01).
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The DJ40 describes the reactive capacity of the neuromuscular system of the player. This factor, generally referred to as stretch-shortening cycle, reveals an ability related to storage of elastic energy during pre-stretch and its release (Verkhoshansky, 1988). Performance in DJ40 showed better results than those of previous studies. Goalkeepers were significantly better (P<0.05 vs DF; P<0.01 vs MF and FW) than the other groups who have researched similar data. This analysis confirmed the usual lack of eccentric loading for playing in outfield positions. Concerning the multiple jump protocol, 15J evaluates the resistive capacities of the knee extensors. Values obtained for the four

groups were similar with those reported by Bosco (1990), both in height and power. Comparisons between position revealed differences: GK and DF groups were significantly better than MF and FW (Fig. 4). Due to the stretch-shortening loads employed during intense actions such as sprinting and jumping during games play, it is thought that plyometric training would be of benefit to soccer players. An adequate training programme can develop jumping ability.