Muscle activity patterns in imitation ski jumps

Abstract

The performance of the take-off in ski jumping creates high demands on the athlete’s neuromuscular system and is associated with the length of the jump. However, investigations of muscle activity during take-off are limited to a few qualitative analyses as summarized by Schwameder (2008). A principal component analysis (PCA) can quantify relevant activation patterns across the measured muscles. For examples, Olree and Vaughan (1995) examined muscle coordination patterns during locomotion. The aim of this study was to examine muscle coordination patterns in imitation ski jumps using PCA.
EMG of eight leg muscles was recorded during imitations ski jumps from a fixed surface and a rolling platform (Ettema, Hooiveld, Braaten & Bobbert, 2016). PCA was conducted on the EMG across the eight muscles for each condition separately. PCA detected for both conditions two relevant muscle activation patterns explaining up to 80% of the EMG signal. The first component (PC1) significantly loaded on calf muscles and leg extensors and indicated muscle coordination at take-off. The handling of balance during take-off could be extracted from the second component (PC2). Small differences between conditions could be found in the weighting coefficients of PC1. The muscle activation pattern of jumping from a rolling platform had higher loads of hip and thigh muscles and lower loads of calf muscles. The results provide insight into muscle coordination of imitation ski jumps. Limitations such as the footwear and the sample size highlight the
importance of further investigations of muscle activity in actual and imitation ski jumping.