The effect of elastic backboards on kinematic and neuromuscular parameters in Para-alpine sit skiers with severe disabilities

Alpine sit skiing is a Winter Paralympic event, in which para-athletes ski sitting on a sit-ski due to physical impairments. Since assistive devices and trunk function play an important role in sit skiers, this single-subject study aims to estimate the effect of elastic backboards on the kinematic and trunk neuromuscular parameters of para-alpine sit skiers. A set of trunk function testing devices and a markerless OpenPose motion tracking system were developed. An experiment, including six different trunk exercises in a sitting position, was conducted on the test board for four para-alpine sit skiers with severe disabilities (LW10-1, LW10-2 × 2, LW11). The controlled experimental condition was whether there was an elastic backboard. The following parameters were recorded and calculated, including joint angular positions, and surface electromyography of trunk muscles (RA, rectus abdominis; EO, external oblique; ES, erector spinae). The multi-joint coordination of the subjects during sitting lateral flexion (SLF) exercises was extracted using a principal component analysis of the joint angles. The results showed that after adding the elastic backboard, the maximal test board inclination angles, the trunk forward flexion angles and the backward extension angles increased by 48.31%, 156.15% and 76.01% respectively. Mean peak activation of EO and ES showed an overall decrease of 23.06% and 28.56% across six exercises. Multi-joint coordination and a weight shift from the upper extremity compensation to hip joints (+46.56%) after adding the elastic backboard were found in the SLF exercise. The above results illustrated the positive influence of the elastic backboard on the kinematic and neuromuscular performance of sit skiers. The findings can support the optimized design of sit-skis and assistive devices in general, and facilitate the application of markerless motion-tracking systems in medical measurements and sports biomechanics.