Association of multi-phase rates of force development during an isometric leg press with vertical jump performances.

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 (ρxy/z = 0.19-0.36, p ≤ 0.004), IRFDs during onset to 100 ms were correlated with RJAS-JH and RJAS-RSI (ρxy/z = 0.33-0.36, p < 0.001), and IRFD during onset to 50 ms was only correlated with RJAS-CT (ρxy/z = -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.

Effects of progressive weight addition using vests on rebound jump.

BACKGROUND: Rebound jump (RJ) is an exercise that is as short contact time and high as possible and is used to improve lower limb stretch-shortening cycle movements. This study examined the effects of RJ performance and lower limb joint kinetics when weight was incrementally added using a weighted vest. METHODS: Eleven male athletes (mean±standard deviation: age, 21.9±1.6 years; height, 176.3±5.5 cm; weight, 67.8±4.2 kg) performed RJ at 0% (no load), 5%, 9%, 12%, 15%, 18%, and 21% added weight. Body coordinates and ground reaction force were measured, and RJ index (jump height / contact time) and joint kinetics (joint torque, power, and work) were calculated. RESULTS: One-way Analysis of Variance showed that the RJ was significantly reduced starting from 12% (P<0.01), the jump height was significantly decreased starting from 12% (P<0.01), and the contact time was significantly increased only at 21% (P<0.01) compared with 0%. The negative peak power of the ankle joint decreased by 21% of the added weight (P<0.01). The main effects of body weight on the peak torque at the knee and hip joints and the positive peak power at the knee joint were observed. CONCLUSIONS: RJ with increasing weight tended to decrease jump height first, rather than longer contact time. However, it was suggested that there is an appropriate range of added weights that can be trained without decreasing the RJ index.

Characteristics of three lower limb joint kinetics affecting rebound jump performance.

The stretch-shortening cycle (SSC) motor execution ability of the lower limb was measured using the rebound jump index (RJ-index) in RJ test; this performance is influenced by the interaction of the forces exerted by the three joints of the lower limb.We aimed to determine RJ performance variables and identify the lower limb kinetic variables that affect them. One hundred two female university students (age, 20.1±1.0 years; height, 164.6±7.2 cm; mass, 58.9±7.3 kg) for whom RJ performance variables (RJ-index, jump height, and contact time) and joint kinetics (torque, power, and work) were measured. Statistical analysis showed a strong correlation between the RJ-index and jump height or contact time (r = 0.920, -0.726, p < 0.05) but a weak correlation between the jump height and contact time (r = -0.384, p < 0.05). Furthermore, positive ankle power was the most influential factor for RJ performance variables; additionally, positive knee power and hip work and eccentric knee torque significantly influenced jump height, and positive ankle power, negative work and power, and concentric torque significantly influenced the contact time. The acquisition of the jump height and a shorter contact time requires different kinetic variables. Furthermore, the characteristics of the force exerted by the three joints of the lower limb that compose the RJ-index may be different even if the RJ-index has the same value. Therefore, by assessing not only the RJ-index but also the jump height, contact time, and characteristics of lower limb joint kinetics in the RJ test, it is possible to conduct effective training to improve lower limb SSC motor execution performance according to individual characteristics.