MOTOR UNIT SYNCHRONIZATION AND FIRING RATE CORRELATE WITH THE FRACTAL DIMENSION OF THE SURFACE EMG: A VALIDATION STUDY

Beretta Piccoli, Matteo and Cescon, Corrado and Vistarini, Ausilia and Pisegna, Caterina and Vannini, Beatrice and Zampella, Cristian and Calanni, Luca and Soldini, Emiliano and D'Antona, Giuseppe (2023) MOTOR UNIT SYNCHRONIZATION AND FIRING RATE CORRELATE WITH THE FRACTAL DIMENSION OF THE SURFACE EMG: A VALIDATION STUDY. In: 12a Giornata della ricerca dell’Innovazione in Medicina della Svizzera Italiana, September 8, Lugano.

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Abstract

Introduction The fractal dimension (FD) of the surface electromyographic (EMG) signal has been reported to be influenced by changes in the firing rate and synchronization of motor units. The purpose of this study was to validate these relations during experimental signals. Methods Thirteen healthy subjects (12 men and 1 woman) performed an isometric knee extension at 5 % of their maximal voluntary contraction for 300 s. Intramuscular and surface EMG signal were recorded concurrently from the vastus medialis obliquus. Synchronization and firing rate were calculated from the decomposed intramuscular EMG signal, while FD was estimated using the box-counting method. The first and last 50 s of contractions were considered during the correlation analyses. Results FD was negatively related to the level of motor unit synchronization (rs = −0.30; p < 0.05) and positively correlated with firing rate (rs = 0.25; p < 0.01) when all data were pooled. FD was correlated with firing rate only during the initial 50 s of contraction (rs = 0.52; p < 0.001). Conclusions FD of the sEMG signal is a parameter mostly related to the firing rate when fatigue does not develop and may 6464c06d59d0e sended: 17 Maggio 2023 be considered as an index of performance fatigability during sustained or at the end of prolonged contractions at very low forces. Indeed, FD cannot be considered as an exclusive index of motor unit synchronization during fatiguing contractions, but rather as largely related to central factors.

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