Terrain stiffness and ankle biomechanics during simulated half-squat parachute landing

Background: A hard surface is potentially one of the risk factors for ankle injuries during parachute landing, but this has never been experimentally validated. This study was designed to evaluate the effects of terrain stiffness on ankle biomechanics during half-squat parachute landing (HSPL). Methods: Eight male and eight female healthy participants landed on three surfaces with standard HSPL technique. The three surfaces were cushioned mats with different thicknesses (0 mm, 4 mm, and 8 mm). The effects of terrain hardness and gender and their interaction with ground reaction forces, ankle kinematics, and electromyograms of selected lower-extremity muscles were statistically analyzed with multivariate analysis of variance. Results: The effects of terrain stiffness and the interaction between factors on all variables were not statistically significant. The effects of gender were not statistically significant on most variables. The peak angular velocity of the ankle dorsiflexion was signifi-cantly lower in men (mean 1345°·s^-1) than in women (mean 1965°·s^-1). A spongy surface even eliminated the differences between men compared to women in the activity of their tibialis anterior during simulated HSPL. Discussion: Terrain stiffness, in the ranges tested, did not appear to influence ankle biomechanics among individuals performing HSPL. Additional studies are required to know whether this finding is applicable to realistic parachuting.