Surface electromyographic inter-individual variability and pattern recognition in front crawl swimming

BACKGROUND AND AIM: Amplitude analysis of electromyography (EMG) has been used to evaluate swimming technique but the variability of EMG recordings is a complex phenomenon rarely examined in this sport. The purposes of this study were to investigate inter-individual variability in muscle activation patterns during front crawl swimming and to explore if there were clusters of sub patterns present. METHODS: Bilateral muscle activity of rectus abdominis (RA) and deltoideus medialis (DM) was recorded using wireless surface EMG in 15 adult male competitive swimmers during three trials of 12.5 m front crawl at maximal speed without breathing. The median EMG trial of six upper limb cycles was used for the interindividual variability assessment, quantified with the coefficient of variation, coefficient of quartile variation, variance ratio and mean deviation. Key features, i.e., sections of the EMG curve selected based on their potential to differentiate between muscle patterns and therefore to potentially classify the EMG patterns in clusters of swimmers, were selected based on qualitative and quantitative classification strategies to enter in a k-means cluster analysis. RESULTS: Inter-individual EMG variability in swimming was higher compared to what has been described for other cyclic movements, but when clustering swimmers, variability dropped in all measures with increased levels (clusters) with the exception of variance ratio for left DM (Table 1). Overall variability and variability in the clusters in RA was higher than in DM. In RA, clusters were differentiated by activity in the recovery phase and around the transition of pull to push phase. In DM, distinction was made by activity in the entry phase and during the exit and early in the recovery phase. CONCLUSIONS: Interindividual variability in a group of highly skilled swimmers was higher compared to other cyclic movements, which is in contrast with what has been reported in the previous 50 years of EMG research in swimming. In front crawl swimming there is not one general activation pattern for DM and RA, but several sub-patterns are present which are statistically different from each other during specific parts of the stroke cycle, mainly due to differences in amplitude. This leads to the conclusion that coaches should be very careful in using overall reference EMG information to enhance the technique of their swimmers. The present findings suggest that individual characteristics could be of more importance in determining the optimal muscle use pattern with the perspective of increasing performance on one hand or decreasing the risk of injuries on the other hand. The detection of these crucial individual characteristics could be a subject of future studies.status: publishe