Trunk kinematics during cross country sit-skiing ergometry

Since trunk function plays a major role in propulsion in sit-skiers and athletes belonging to distinct classes have different abilities to control trunk muscles, the aim of this study is to evaluate how athletes personalized their skiing strategy to compensate their impairment and improve skiing effectiveness. Sixteen Paralympic sit-skiers belonging to different classes volunteered as participant. Each athlete executed two double poling tests on a ski ergometer at the maximal speed he/she can reach and the best, identified as the fastest, was considered in the analysis. A set of two passive reflective markers was used for kinematic analysis: the first marker was placed on the athlete shoulder, while the second was placed on the sledge in correspondence of the hip joint. A Vicon motion capture system with 8 cameras was used to collect the athlete's motion during the double poling tests. Forces were recorded by sensors attached to the pulling cables. For the analyses athletes were grouped concerning to the individual impairment level into: group A (LW10-LW10.5), group B (LW11-LW11.5), and group C (LW12). Per each athlete the trunk maximal forward and trunk maximal backward, the range of motion, the start and finish time of trunk movement with respect to the beginning of the poling phase were measured during each cycle, and the time between the start and the finish of trunk movement were calculated. The main results of this study were: 1) greater trunk flexion and range of motion for group C compared to group A; 2) group A started trunk movement earlier compared to group C; 3) no differences in range of motion timing. Since greater trunk flexion and range of motion allow generating higher propulsion force with low level of fatigue, it is possible to conclude that thanks to their ability in control trunk muscles athletes in group C can develop a skiing strategy which is more effective than athletes that cannot control abdominal and lumbar extensor muscle