Association of multi-phase rates of force development during an isometric leg press with vertical jump performances2024 · Purpose This study aimed to elucidate characteristics of explosive force-production capabilities represented by multi-phase rate of force developments (IRFDs) during isometric single-leg press (ISLP) through investigating relationships with countermovement (CMJ) and rebound continuous jump (RJ) performances. Methods Two-hundred-and-thirty male athletes performed ISLP, CMJ with an arm swing (CMJAS), and RJ with an arm swing (RJAS). IRFDs were measured during ISLP using a custom-built dynamometer, while CMJAS and RJAS were measured on force platforms. The IRFDs were obtained as rates of increase in force across 50 ms in the interval from the onset to 250 ms. Jump height (JH) was obtained from CMJAS, while RJAS provided JH, contact time (CT), and reactive strength index (RSI) values. Results All IRFDs were correlated with CMJAS-JH (ρ = 0.20–0.45, p ≤ 0.003), RJAS-JH (ρ = 0.22–0.46, p ≤ 0.001), RJAS-RSI (ρ = 0.29–0.48, p < 0.001) and RJAS-CT (ρ = −0.29 to −0.25, p ≤ 0.025). When an influence of peak force was considered using partial rank correlation analysis, IRFDs during onset to 150 ms were correlated with CMJAS-JH (ρ<sub>xy/z</sub> = 0.19–0.36, p ≤ 0.004), IRFDs during onset to 100 ms were correlated with RJAS-JH and RJAS-RSI (ρ<sub>xy/z</sub> = 0.33–0.36, p < 0.001), and IRFD during onset to 50 ms was only correlated with RJAS-CT (ρ<sub>xy/z</sub> = −0.23, p < 0.001). Conclusion The early phase (onset to 150 ms) IRFDs measured using ISLP enabled the assessment of multiple aspects of leg-extension strength characteristics that differ from maximal strength; these insights might be useful in the assessment of the athletes’ leg-extension strength capabilities.
Kinetic variables of the lower limb joint that affect the drop jump index at different drop heights.2024 · BACKGROUND: The drop jump index evaluates power exertion in the lower limb stretch-shortening cycle. In addition, the ability to exert power during the stretch-shortening cycle can be evaluated in detail by combining the drop jump index with the kinetic variables of the three lower limb joints. The purpose of this study was to determine the kinetic variables of the three lower limb joints during takeoff that affect the drop jump index of a drop jump from different drop heights. METHODS: In total, 100 male athletes performed drop jumps from three drop heights (0.3, 0.6, and 0.9 m). Drop jump index and kinetic variables (torque, power, and work) of the three lower limb joints were calculated using body coordinates by infrared camera, and ground reaction force data by force plate. Multiple regression analysis was used to examine the parameters by which the kinetic variables of the three lower limb joints affected the drop jump index. RESULTS: As a result, ankle joint and knee joint positive power were extracted as parameters affecting drop jump index at 0.3 m. In addition to these parameters, ankle negative power, ankle negative work and hip eccentric torque at 0.6 m, and knee eccentric torque at 0.9 m were extracted as parameters affecting the drop jump index. CONCLUSIONS: These results suggest that a higher drop height leads to a greater effect of eccentric torque exertion at the knee and hip joints and of positive power at the ankle and knee joints on the acquisition of the drop jump index.
