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.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.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).FD of the sEMG signal is a parameter mostly related to the firing rate when fatigue does not develop and may 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.

Motor unit synchronization and firing rate correlate with the fractal dimension of the surface EMG: A validation study

D'Antona, Giuseppe
2023-01-01

Abstract

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.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.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).FD of the sEMG signal is a parameter mostly related to the firing rate when fatigue does not develop and may 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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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11571/1490798
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