Ground reaction forces measurement based on strain gauges in alpine skiing

Ski experts in technique of turning on skis are dealing with problems concerning load of skis during particular kinds of joined curves. There are many theoretical works, most of them based on kinematographic or dynamographic record or on a combination of both methods. Observation of reaction forces between the ski and the plate has been performed in the past. Many studies have been performed to eliminate the number of injuries of knee-joints. However, significant changes occurred in the construction of skis and ski boots in recent years. Also a shift to the use of carving skis appeared. With such a way of skiing, bigger side-cut radius is exploited than it was with the traditional skis. This is the reason, why recently the number of studies dealing with biomechanics of alpine skiing with emphasis on measurement of trajectory and ground reaction forces. We have developed a special measuring device, which enables to measure forces in three directions and also their torsional moments around these three axis. This system works on the principle of strain gauges. During the measurement all the data are collected on Compact Flash disc with the frequency of 100 Hz. We were interested whether it is possible with help of the system, to detect interindividual deviation during a carve and thus to participate on improving of skiing technique. Our measurement refered to measurement of ground reaction forces arising during a carving turn. The investigation was carried out on a group of 6 skiers (3 racers and 3 ski teachers) with the weight of M = 78,8 +/- 5,46 kg. Their height was M = 1,80 +/- 0,04m and age was M = 26,5 +/- 1,61 years. We realised that during a carving turn the strongest ground reaction forces occur during the steering phase after the fall line and during the initiation phase skis are alleviated and edging is changed. It was interesting that from the point of view of ground reaction forces there is no identical pass of right and left turn from all measured skiers. Comparison of measured left carving turn and comparison of right carving turn showed very similar cycle. Ground reaction forces measurement has already become a part of preparation of advanced national teams and it can help to improve quality of skiing not only top-class skiers, but also coaches of young gifted individuals can contribute to quick progress in technical performance of some motoric activities owing to measured data.