Abstract
At relatively low effort level tasks, surface electromyogram (sEMG) spectral parameters have demonstrated an inconsistent ability to monitor localized muscle fatigue and predict endurance capacity. The main purpose of this study was to assess the potential of the endurance time (Tend) prediction using logarithmic parameters compared to raw data. Ten healthy subjects performed five sets of voluntary isotonic contractions until their exhaustion at 20% of their maximum voluntary contraction (MVC) level. We extracted five sEMG spectral parameters namely the power in the low frequency band (LFB), the mean power frequency (MPF), the high-to-low ratio between two frequency bands (H/L-FB), the Dimitrov spectral index (DSI), and the high-to-low ratio between two spectral moments (H/L-SM), and then converted them to logarithms. Changes in these ten parameters were monitored using area ratio and linear regressive slope as statistical predictors and estimating from onset at every 10% of Tend. Significant correlations (r > 0.5) were found between log(Tend) and the linear regressive slopes in the logarithmic H/L-SM at every 10% of Tend. In conclusion, logarithmic parameters can be used to describe changes in the fatigue content of sEMG and can be employed as a better predictor of Tend in comparison to the raw parameters.
Highlights
In everyday life, low-moderate level isotonic exercise is the natural way of human activity and includes a concentric contraction and an eccentric contraction
SEMG has been shown to be a more objective approach to measuring muscle fatigue which is generally accompanied by an increase in amplitude of the surface electromyography (sEMG) signal because of the firing rates of increased motor unit recruitment [13,14]
The experimental result obtained showed that linear regressive slopes of high-to-low ratio between two spectral moments (H/L-SM) over the first 30% of Tend were significantly correlated with Tend [21,22,23]
Summary
Low-moderate level isotonic exercise is the natural way of human activity and includes a concentric contraction and an eccentric contraction. Endurance capacity is the ability to sustain a given force over time, while measurement of the endurance time (Tend) is an indicator of the muscle resistance to fatigue [4,5,6]. A lot of researchers have studied endurance time prediction due to the fact that firing statistics of the active motor units (MU) were shown to affect the sEMG power spectrum toward lower frequencies as spectral compression [9,10,11,12]. Maïsetti et al (2002) demonstrated that the area ratio which was proposed by Merletti et al (1991) as changes of the low frequency band (LFB), as estimated around the first 25% of Tend, were significantly correlated with Tend. The experimental result obtained showed that linear regressive slopes of H/L-SM over the first 30% of Tend were significantly correlated with Tend [21,22,23]
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