The Influence of Trunk Impairment Level on the Kinematic Characteristics of Alpine Sit-Skiing: A Case Study of Paralympic Medalists

Abstract

This study aimed to examine the relationship between the trunk impairment level and the trunk kinematic characteristics during alpine sit-skiing from a classification perspective. Three Paralympic medalists in sitting classes (LW10-2, LW11, and LW12-2) participated in the present study. To simulate the racing conditions, giant slalom gates were set. To measure the kinematics of the skier and sit-ski during skiing, a motion capture method with inertial measurement units was used. The muscle activities of the trunk muscles were evaluated using electromyography. Chest lateral flexion, chest flexion, and hip flexion/extension angle during sit-skiing were reduced due to impairment. Additionally, the insufficient lateral flexion (angulation) caused a decrease in edging angle, and that the insufficient chest and hip flexion/extension caused a lower loading in the latter half of the turn through smaller vertical movement. Since edging angle and loading are key factors in ski control, the three joint motions could be measures of sport-specific activity limitation in sit-skiing classification. Between the LW10-2 and LW11 skiers, no distinct differences in trunk kinematics were found. Assuming the scaling factor of race time as a measure of skiing performance, one possible reason is that the difference in skiing performance the LW10-2 and LW11 skiers is considerably smaller relative to differences between the LW11 and LW12-2 skiers. There were no distinct differences among classes in the results of muscle activity, and therefore, this information appears to play a minimal role for classification.

Cluster analysis of multiple impairment measures in evidence‐based classification for para‐alpine sit skiers

“…Based on previous studies on alpine sit skiing biomechanics 6,20 and recommendations from other sitting sports, 9,10 the maximum isometric trunk muscle strength was evaluated using forward, left, and right trunk flexion tests. Similar equipment and set‐up described in previous studies have been used in these tests 9,10,21 .…”

“…To measure the determinants of alpine sit skiing performance, a board tilt test (simulated skiing test) was performed, which simulated the snowboard carving turns during para‐alpine skiing 6 . This was one of the standardized tests in the current IPC classification guide 4 .…”

“…They typically have strength impairments in all trunk muscles, including the rectus abdominis (RA) and erector spinae (ES), and are unable to sit unsupported. Class LW12‐2 is for athletes with impairments that cause minimal activity limitations in alpine sit skiing (e.g., below‐knee amputation) and who have full trunk function 4,6 . The traditional classification relies on the opinion of expert classifiers, which may involve subjective decision‐making related to experience.…”

“…In para‐alpine skiing, sit skiers relied on their trunks to control sit‐skis and change their anteroposterior and lateral center of mass to complete turns 17–19 . The turning performance depends on the control of the edging angle between the ski board and the snow surface, which could be a measure of alpine skiing performance 6,20 . Given the difficulty and complexity of outdoor testing, measures of alpine skiing performance could be simplified, and standardized in simulated skiing tests indoors.…”

“…[17][18][19] The turning performance depends on the control of the edging angle between the ski board and the snow surface, which could be a measure of alpine skiing performance. 6,20 Given the difficulty and complexity of outdoor testing, measures of alpine skiing performance could be simplified, and standardized in simulated skiing tests indoors. For instance, the fifth test in the IPC classification rules requires the athletes to tilt a testing board in a sitting position from side to side like carving a snowboard on snow.…”