Intra-Individual Variability of Surface Electromyography in Front Crawl SwimmingReport as inadecuate

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The variability of electromyographic EMG recordings between and within participants is a complex problem, rarely studied in swimming. The importance of signal normalization has long been recognized, but the method used might influence variability. The aims of this study were to: i assess the intra-individual variability of the EMG signal in highly skilled front crawl swimmers, ii determine the influence of two methods of both amplitude and time normalization of the EMG signal on intra-individual variability and of time normalization on muscle activity level and iii describe the muscle activity, normalized using MVIC, in relation to upper limb crawl stroke movements. Muscle activity of rectus abdominis and deltoideus medialis 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. Two full upper limb cycles were analyzed from each of the swimming trials, resulting in six full cycles used for the intra-individual variability assessment, quantified with the coefficient of variation CV, coefficient of quartile variation CQV and the variance ratio VR. The results of this study support previous findings on EMG patterns of deltoideus medialis and rectus abdominis as prime mover during the recovery 45% activity relative to MVIC, and stabilizer of the trunk during the pull 14.5% activity respectively. The intra-individual variability was lower VR of 0.34–0.47 when compared to other cyclic movements. No meaningful differences were found between variability measures CV or VR when applying either of the amplitude or the time normalization methods. In addition to reporting the mean amplitude and standard deviation, future EMG studies in swimming should also report the intra-individual variability, preferably using VR as it is independent of peak amplitude, provides a good measure of repeatability and is insensitive to mean EMG amplitude and the degree of smoothing applied.

Author: Jonas Martens , Daniel Daly, Kevin Deschamps, Ricardo Jorge Pinto Fernandes, Filip Staes



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