The influence of midsole density and arch height on the biomechanics of plyometric drop jumps

Little is known of the individual and/ or interactive effects of midsole density and arch height on forefoot activities such as landing and jumping. Therefore, the purpose of this study was to examine the effects of shoe midsole density and arch height on the biomechanics of drop jumps. Fifteen healthy males (age: 22.6 ± 4.52 yrs, body mass: 84.77 ± 12.27 kg, height: 1.83 ± 0.06 m) participated in this study. An arch height ratio was calculated on the subjects' left foot to divide them into high (n = 7) and low (n = 8) arch groups. Subjects were tested during the drop jumps in three pairs of basketball shoes (adidas) with different midsole density (soft, normal and hard). At the initiation of testing, subjects were tested on maximum vertical jump height (MVJH) with countermovement wearing the normal midsole shoes to determine their drop heights (33, 66, and 100% of MVJH). Subjects performed five drop-jump trials in each of nine conditions (3 midsoles x 3 heights) with shoes randomized at each height. Simultaneous recording of sagittal kinematics (120 Hz) and ground reaction forces (GRF, 1200 Hz) were collected. A Shannon algorithm was used to reconstruct the video signal from 120 Hz to 240 Hz. A mixed 2 x 3 x 3 (group x density x height) repeated measures analysis of variance was performed on selected GRF and kinematic variables within each group with the significance level set at p < 0.05. A significant height main effect was observed for all variables. Peak GRF in the landing (LMax) was significantly lower for the hard midsole compared to the other midsoles for both groups. Ankle angular kinematics revealed greater values for contact angle, contact velocity, and maximum velocity in the landing phase for the low arch subjects. Joint kinetics revealed significant total work differences between groups at the hip and knee. The high-arch subjects tended to use their hips more than their knees compared to the low arch subjects. The results suggest that significant differences do exist in the biomechanical characteristics of the drop jump for subjects with different arch heights