The purpose of this study was to determine the effects of plyometric exercise (depth drops), combined with weight training, on dynamic leg strength and leg power. Plyometrics are exercises that force a rapid lengthening of muscle prior to contraction, to result in increased force output during contraction. Thirty-one volunteer university students were randomly assigned to three groups according to height of drop (1.1 m=high, 0.4 m=low and no height). Subjects in each group were classified in two conditions according to leg strength-body weight ratio (low=less than 2, and high=greater than 2). All groups were administered a dynamic leg strength test and Magaria anaerobic power test prior to and following an eight-week plyometric and weight training program. A two-way ANOVA (groups (3) x conditions (2)) revealed no significant differences between groups, conditions, and no significant interactions for leg strength and Magaria power scores. Independent T-tests for mean differences between pre- and post-test scores demonstrated significant gains in both strength and power for each group. It was concluded that participating in a combined 8-week program of plyometrics and weight training will improve leg strength and power. Furthermore, coaches and athletes should be apprised that neither the level of strength nor height of drop variables altered the resultant training effects of the combination program used in this study. The possibility of reducing the time between forced stretch at impact and initiation of contraction to improve plyometric training effects was discussed.
(C) 1987 National Strength and Conditioning Association