Explosive strength deficit as a predictor of vertical jumping performance

Currently, variables predictive of vertical jumping performance can account for only part of its total variability. A potential additional source of variation called explosive strength deficit (ESD) was described in 1995 by Zatsiorsky (Science and Practice of Strength Training. Champaign, IL: Human Kinetics, 1995. pp. 34-35.). ESD is determined by measuring the maximum force generated under ideal circumstances (F(mm)) and under task-relevant conditions (F(m)). It is calculated as 100(F(mm) - F(m))/F(m). For this study, the following operational definitions were used: F(mm) = squatting peak force at 0.51 m x s(-1); F(m) = squatting peak force at 1.43 m x s(-1). Data were analyzed using forward stepwise multiple regression. Mean ESD for men was 29.7% (SD = 11.7) and for women was 49.3% (SD = 11.2). For men and women, respectively, zero-order correlations for ESD with restricted vertical jumping (RVJ) distance were -0.35 and -0.60, and between ESD and drop vertical jumping (DVJ) distance were -0.20 and -0.63. However, when the previously identified predictors were taken into account, ESD was not a significant predictor (p > 0.05) of either type of jump. Therefore, it was concluded that ESD on the basis of velocity-regulated squats does not augment the explained variance previously established for vertical jumping performance.