Analysis of inter-segment coordination during the take-off of ski jumping

In ski jumping, take-off (TO) is considered as the most important phase. While spatio-temporal features have been identified during this phase, inter-segment coordination has never been investigated. This study proposed a new method using body worn inertial sensors to reliably determine the inter-segment coordination during TO. For this purpose, the continuous relative phase (CRP) was calculated for thigh-shank and sacrum-thigh segments pairs during TO from the inertial signals over 86 jumps of 32 athletes (Figure 1). Then, key coordination features were extracted from CRP and compared to performance, scored by a distance score, using regression analysis. The CRP curves indicated a repeatable pattern with characteristic features (coefficient of multiple correlation of 0.85 for thigh-shank and of 0.96 for sacrum-thigh). The features proposed in this study reported a high potential for performance evaluation. The mean CRP for the thigh-shank pair and the temporal occurrence of the minimum for the thigh-shank pair and of the maximum for the sacrum-thigh pair were particularly relevant. In summary, the athletes who obtained a higher distance score showed a shank leaded by the thigh in phase domain as long as possible during TO and were able to precisely tune the coordination between thigh and sacrum.