Unexperienced mechanical effects of muscular fatigue can be predicted by the Central Nervous System as revealed by anticipatory postural adjustments

Abstract

Muscular fatigue effects have been shown to be compensated by the implementation of adaptive compensatory neuromuscular strategies, resulting in modifications of the initial motion coordination. However, no studies have focused on the efficiency of the feedforward motor commands when muscular fatigue occurs for the first time during a particular movement. This study included 18 healthy subjects who had to perform arm-raising movements in a standing posture at a maximal velocity before and after a fatiguing procedure involving focal muscles. The arm-raising task implies the generation of predictive processes of control, namely Anticipatory Postural Adjustments (APAs), whose temporal and quantitative features have been shown to be dependent on the kinematics of the upcoming arm-raising movement. By altering significantly the kinematic profile of the focal movement with a fatiguing procedure, we sought to find out whether APAs scaled to the lower mechanical disturbance. APAs were measured using surface electromyography. Following the fatiguing procedure, acceleration peaks of the arm movement decreased by ~27%. APAs scaled to this lower fatigue-related disturbance during the very first trial post-fatigue, suggesting that the Central Nervous System can predict unexperienced mechanical effects of muscle fatigue. It is suggested that these results are accounted for by prediction processes in which the central integration of the groups III and IV afferents leads to an update of the internal model by remapping the relationship between focal motor command magnitude and the actual mechanical output.

Electrically-induced muscle fatigue affects feedforward mechanisms of control

“…Decreased flexion peak accelerations were more difficult to obtain with EMS as compared to voluntary contractions (-12% here vs. -27% in Monjo and Forestier, 2014). This can be accounted by the fact that EMS only activates (and thus fatigue) the superficial parts of muscles.…”

“…This can be accounted by the fact that EMS only activates (and thus fatigue) the superficial parts of muscles. Besides, the procedure used in the present study selectively targeted two of the muscles involved in arm flexion while voluntary contractions such as the ones used in Monjo and Forestier (2014) enable to recruit (and thus fatigue) all the synergist flexion muscles, i.e.…”

“…Indexes referring to the ability to manage the self-generated perturbation by relating focal to postural parameters have already been employed in the literature (Bouisset and Do, 2008;Monjo et al, 2014).…”

“…Pre and post-fatigue, they achieved MVF tests and MVC of the Anterior Deltoid and Medial Deltoid during which we recorded the EMG signals. The MVF tests were carried out in the same way than in Monjo et al (2014). Given that only 3 subjects achieved the EMS procedure, only the mean values ± SEM will be presented in the result part.…”

“…When efficiently induced, muscle fatigue of a moving limb has been shown to result in significant alterations of the acceleration-generating capacity (Jaric et al, 1997;Corcos et al, 2002;Monjo and Forestier, 2014). During self-paced arm flexions performed at maximal velocity following an isometric fatiguing procedure of the arm flexors, it appears that the CNS is able to accurately predict the mechanical effects of muscle fatigue (Monjo and Forestier, 2014). Indeed, in this study, decreased APAs scaling to the lower postural disturbance were observed during the very first trial post-fatigue, suggesting that forward models incorporate fatigue signals into prediction processes.…”