Muscle Activity and Morphology in Slalom Skiing by a Single-Leg Amputee Ski Racer: A Case Study of a Paralympic Athlete

The aim of this study was to clarify the characteristics of skiing by a single-leg amputee ski racer from the viewpoints of muscle activity, morphology, and the relationship between both elements through comparisons with those of a non-disabled ski racer. One elite athlete, classified as LW2 (left thigh amputation), and one non-disabled athlete, as a control, participated in this study. The cross-sectional area of thigh muscles was measured through magnetic resonance imaging. Additionally, muscle activities and joint and segment kinematics during slalom skiing were measured using electromyography and inertial measurement units, respectively. The muscle activities and joint kinematics of the amputee racer in the turn in which he performed with the inside edge of the ski were similar to those of the outside leg of the non-disabled racer over a turn. In contrast, at the turn in which the amputee racer performed with the outside edge (more difficult side), the amputee racer largely activated the biceps femoris (BF) in the first half of the turn compared to the non-disabled racer. The reason could be to control the angular momentum of the trunk during the forward tilting motion. This is because a greater activity of the BF was observed during the period in which the forward tilt of the trunk was increased, and the mean activity of the BF was the greatest during the first half of the right turn in which the range of the motion of the forward tilt was the greatest. In terms of muscle morphology of the amputee racer, a significant hypertrophy of the BF and vastus lateralis was observed compared to the non-disabled racers. The well-developed BF was considered to be related to the large activity during the turn performed with the outside edge of the ski