Purpose: Maximal muscle strength is often assessed with single-joint or repetition-maximum testing. The purpose of this study was to evaluate the reliability of countermovement-jump (CMJ) velocity-load testing and assess the relationship between CMJ velocity-load kinetics and concentric-isometric-eccentric multijoint leg-extension strength tested on a robotic servomotor leg press in trained athletes. Methods: University athletes (N = 203; 52% female) completed 3 concentric, isometric, and eccentric maximum voluntary leg-extension contractions on the robotic leg press, followed by CMJ velocity-load testing with an additional external load of 0% (CMJBW), 30% (CMJ30), and 60% (CMJ60) of body mass. A linear model was fit for the CMJ takeoff velocity-load relationship to obtain the load intercept. Force-velocity parameters were obtained for the CMJ eccentric deceleration and concentric phases. Linear mixed-effects models were constructed to predict concentric, isometric, and eccentric leg-press force using the CMJ takeoff velocity-load relationship and CMJ kinetics. Results: Isometric leg-press strength was predicted by load intercept and sex (P < .001, R2 = .565, prediction error = 14%). Concentric leg-press strength was predicted by load intercept, CMJ60 concentric impulse, and sex (P < .001, R2 = .657, prediction error = 10%). Eccentric leg-press strength was predicted by minimum downward velocity, CMJ60 eccentric deceleration impulse, and sex (P < .001, R2 = .359, prediction error = 14%). Conclusions: Given the relevance of muscle-strength testing for sport performance and injury prevention, assessing force-velocity mechanics with loaded CMJ testing is a reliable and viable approach to predict maximal concentric, isometric, and eccentric leg-press strength in competitive athletes.
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