In contrast to the drop in the incidence of fractures of the lower leg, or tibia, that has been observed in recent years, the incidence of knee injuries has not decreased in skiing and there has been a relative increase in the frequency of severe knee lesions and of the isolated rupture of the cruciate ligament, prompting us to conduct a comprehensive study of the causes of these phenomena. It was found necessary to develop a innovative method of measurement to analyse the patterns of movement and stress to which the knee injuries were attributed. By combining and synchronizing movement analysis, measurement of pressure distribution and measurement of force it became possible to perform a detailed analysis of the forward/backward movement in the ski boot in the laboratory and also on the course by telemetry (part 1). The first two studies were devoted to the forward lean in the ski boot (part 2). Basing on movement analysis and simultaneous determination of pressure distribution along the lower leg, the influence of different ski boot models on the Vorlage, or forward lean, movement of beginners and very experienced skiers was studied. An important result of the laboratory experiment was that whereas a ski boot can be moved without difficulty into a strong forward lean position of the skier by an experienced sportsman, a beginner can only assume a forward lean with 20% less inclination (this being a significant difference). In other words: the range of the freedom of movement in such a boot is markedly limited. The assumption that in ski amateurs such a ski boot would promote skiing in backward lean position, was confirmed by studies on the course (part 3). The pupils became definitely less adept at learning if they were required to wear a stiff ski boot; analysis of movement showed that the forward lean angles were clearly smaller and that the skiers adopted a skiing style in backward lean position that exercised an undue strain on the knees. The other two studies, therefore, focussed mainly on the backward movement in the ski boot. Specifically, the fixed rear spoilers of the modern ski boots are accused of contributing to the rupture of the anterior cruciate ligament if the skier lands on the tail ends of the skis after a jump or fall in backward lean position ('big bump, flat landing' syndrome).(ABSTRACT TRUNCATED AT 400 WORDS)