A biomechanical approach to paralympic cross-country sit-ski racing.

Objective: To analyze the biomechanics of the double poling (DP) gesture in cross-country disabled sit-skiers in the field during competition.

Design: Cross-sectional research.

Setting: One-kilometer sprint race, Winter Paralympic Games, Vancouver 2010, Canada.

Participants: Paralympic athletes: 35 men and 15 women, classified in all the 5 classes of the sit-skier category.

Intervention: Elite sit-skiers, with different disabilities, were recorded with a high-speed markerless stereophotogrammetric camera system. Reference points were semiautomatically tracked frame-by-frame on video images, according to a biomechanical model consisting of 7 anatomical and 4 technical points.

Main Outcome Measures: Coordinates of anatomical and technical points were evaluated for 2-dimensional kinematic analysis of the push gesture both with reference to a ground-fixed frame and with respect to the athletes' seat on the sledges.

Results: Several graphical results represent the development of the DP gesture of each athlete with respect to both ground reference frame and sledge reference frame. The progression of the gesture is depicted by body and pole stick diagrams, trends of reference point positions and their gradients, and body joint trajectories in space. In addition, kinematic biomechanical parameters (eg, joints' range of motion) and technical parameters (eg, pole incline, sledge velocity) are reported.

Conclusions: This research demonstrates the feasibility of a markerless kinematic analysis of the poling gesture on a contest field. Results point out a wide variability of the gesture due to the residual functional capabilities and sitting postures of each athlete. However, the poling cycles of subjects classified into different classes present similar features. An original segmentation of the DP gesture in a sequence of 3 phases is proposed in the article.