Abstract

Using a measuring system which is described in detail in another paper in this conference, the load on the ski, sole pressure, leg joint motion, and turn direction have been measured during a long turn of an expert skier. The instant of turn change was associated with a change in the sign of the force moment about the ski direction. The total force on the outside ski was generally about double that on the inside ski, while both loads instantly decreased at the turn change. Foot pressure increased at the heel area during the steering process. The center of the pressure was always kept in the rear part near the heel, but it moved forward at the turn change. The main motion of the leg was a combination of flexion-extension of the hip joint, knee joint and ankle joint. The outside leg was kept extended angle during the steering process, while the inside leg gradually flexed and extended. The trajectory of the body was estimated from the data of a magnetic compass at the backpack. The forces, foot pressure, joint motion and body trajectory were compared with the video image of the skier. This comparison showed that the skier made the turn change earlier than the centerline of the turn trajectory. During the turn change process, the skier first extended the previous inside leg without flexing the outside leg. Next, he shifted the main load from the previous outside leg to the other leg, at this time the force moment also changed. Then he flexed the new inside leg. We think that the timing of these motions is the main factor determining the downhill speed achieved. Verf.-Referat