The perpendicular ground reactive force on paratrooper's feet in"straddling"half-squat landing simulation

Abstract

Objective To analyze the characteristics of perpendicular ground reaction force on paratrooper's feet instraddlinghalf-squat parachute landing simulation, and to provide a theoretical basis for further the exploration of parachute landing injury mechanisms and the prevention. Methods Eighteen active service paratroopers, who were wearing Model-06 parachute boots, jumped from 30 cm or 60 cm height and landed on a tri-axial force measuring platform withstraddlinghalf-squat or standard half-squat landing posture. When withstraddlinghalf-squat landing every paratrooper was marked by bigger and smaller force foot according to the measured perpendicular ground reaction force. The forces on feet determined by different jumping height were analyzed by paired sample t-test and those with different landing postures were tested by the analysis of variance. Results ①The difference of maximal perpendicular ground reaction force showed significance between paratrooper's feet as they were instraddlinghalf-squat landing and it got larger with the height increase (t=5.80, 7.31, P<0.01); There also existed significant difference in the maximal action buffer time (P<0.05). The maximal action buffer time of thestraddlinghalf-squat landing was significantly longer than that of the standard half-squat parachute landing (F=11.11, 22.12, P<0.01). Conclusions With thestraddlinghalf-squat landing simulation, paratrooper experience significant different maximal perpendicular ground reaction force on their feet and the difference get bigger as height increased. It indicates that such landing approach can lead to the instability of landing due to the unbalanced forces acted on feet and may easily result in landing injury. Key words: Foot; Ankle injuries; Exercise tests; Aviation; Biomechanics; Half squat parachute landing; Parachute simulation