INVOLVEMENT OF ECCENTRIC MUSCLE ACTIONS IN GIANT SLALOM RACING

Joint angular movements and muscle activation (EMG), were determined i n male elite racers while performing the giant slalom. Movement cycles averaged 3.5 +/- 0.6 s (left plus right turn), and knee angle ranged 66-114 degrees (180 degrees = straight leg). Knee extensor muscle use was dominated (rectified EMG; P < 0.05) by the leg controlling the out side (downhill) ski during the turn. Time spent while decreasing knee angle (eccentric muscle action) of outside leg averaged 1.0 +/- 0.2 s. This phase was longer (P < 0.05) than the average push-off (concentri c muscle action) phase of 0.5 +/- 0.1 s. Moreover, EMG activity of the outside leg during eccentric muscle actions exceeded (P < 0.05) that of concentric actions and was similar to that attained during maximum isometric knee extension in laboratory tests. Knee and hip angular mov ement ranged 20-50 degrees. Average joint velocities equalled 20-40 de grees . s(-1) during the turning phase. Thus, competitive giant slalom skiing is dominated by slow eccentric muscle actions performed at nea r maximum voluntary force. Because of their greater ability to generat e force, eccentric muscle actions may be warranted or even required to resist the G-forces induced during the turn phase.