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This study examined concurrent validity of countermovement vertical jump reactive strength index modified and force-time characteristics recorded using a 1-dimensional portable and laboratory force plate system. Twenty-eight men performed bilateral countermovement vertical jumps on 2 portable force plates placed on top of 2 in-ground force plates, both recording vertical ground reaction force at 1000 Hz. Time to takeoff; jump height; reactive strength index modified; and braking and propulsion impulse, mean net force, and duration were calculated from the vertical force from both force plate systems. Results from both systems were highly correlated (r ≥ .99). There were small (d < 0.12) but significant differences between their respective braking impulse, braking mean net force, propulsion impulse, and propulsion mean net force (P < .001). However, limits of agreement yielded a mean value of 1.7% relative to the laboratory force plate system (95% confidence limits, 0.9%-2.5%), indicating very good agreement across all of the dependent variables. The largest limits of agreement were for jump height (2.1%), time to takeoff (3.4%), and reactive strength index modified (3.8%). The portable force plate system provides a valid method of obtaining reactive strength measures, and several underpinning force-time variables, from unloaded countermovement vertical jump. Thus, practitioners can use both force plates interchangeably.

The aim of this study was to quantify the load that maximized peak and mean power, as well as impulse applied to these loads, during the push press and to compare them to equivalent jump squat data. Resistance-trained men performed two push press (n = 17; age: 25.4 ± 7.4 years; height: 183.4 ± 5 cm; body mass: 87 ± 15.6 kg) and jump squat (n = 8 of original 17; age: 28.7 ± 8.1 years; height: 184.3 ± 5.5 cm; mass: 98 ± 5.3 kg) singles with 10-90% of their push press and back squat 1 RM, respectively, in 10% 1 RM increments while standing on a force platform. Push press peak and mean power was maximized with 75.3 ± 16.4 and 64.7 ± 20% 1RM, respectively, and impulses applied to these loads were 243 ± 29 N.s and 231 ± 36 N.s. Increasing and decreasing load, from the load that maximized peak and mean power, by 10% and 20% 1RM reduced peak and mean power by 6-15% (p < 0.05). Push press and jump squat maximum peak power (7%, p = 0.08) and the impulse that was applied to the A C C E P T E DCopyright Ó Lippincott Williams & Wilkins. All rights reserved.load that maximized peak (8%, p = 0.17) and mean (13%, p = 0.91) power were not significantly different, but push press maximum mean power was significantly greater than the jump squat equivalent (~9.5%, p = 0.03). The mechanical demand of the push press is comparable to the jump squat and could provide a time-efficient combination of lower-body power and upper-body and trunk strength training.