Decelerations of Parachute Opening Shock in Skydivers

INTRODUCTION: High prevalence of neck pain among skydivers is related to parachute opening shock (POS) exposure, but few investigations of POS deceleration have been made. Existing data incorporate equipment movements, limiting its representability of skydiver deceleration. This study aims to describe POS decelerations and compare human- with equipment-attached data. METHODS: Wearing two triaxial accelerometers placed on the skydiver (neck-sensor) and equipment (rig-sensor), 20 participants made 2 skydives each. Due to technical issues, data from 35 skydives made by 19 participants were collected. Missing data were replaced using data substitution techniques. Acceleration axes were defined as posterior to anterior (+a(x)), lateral right (+a(y)), and caudal to cranial (+a(z)). Deceleration magnitude [a(max) (G)] and jerks (G.s(-1)) during POS were analyzed. RESULTS: Two distinct phases related to skydiver positioning and acceleration direction were observed: 1) the x-phase (characterized by -a(x), rotating the skydiver); and 2) the z-phase (characterized by +az, skydiver vertically oriented). Compared to the rig-sensor, the neck-sensor yielded lower a. (3.16 G vs. 6.96 G) and jerk (56.3 G . s(-1) vs. 149.0 G . s(-1)) during the x-phase, and lower jerk (27.7 G . s(-1) vs. 54.5 G . s(-1)) during the z-phase. DISCUSSION: The identified phases during POS should be considered in future neck pain preventive strategies. Accelerometer data differed, suggesting human-placed accelerometry to be more valid for measuring human acceleration.