Cortical short-term fatigue effects assessed via rhythmic brain-muscle coherence

This study is aimed at assessing the short-term effects of muscular fatigue on the sensorimotor areas organization in the left and right hemispheres. Magnetoencephalographic (MEG) and electromyographic (EMG) activities were simultaneously recorded during the execution of a non-fatiguing motor task, performed before and after a task known to induce muscle fatigue (Fatigue). Coherence between cerebral and muscular rhythms as well as cerebral and muscular rhythms spectral densities were estimated during this non-fatiguing task and at rest. The MEG-EMG coherence in the beta band (13-32 Hz) was higher after than before Fatigue. The background activity reduction during contraction with respect to rest (i.e. the cerebral reactivity) was less evident after than before Fatigue in the gamma (33-45 Hz) and beta bands. When differentiating subjects on the base of Fatigue endurance times, while a huge inter-subject variability was found, an evident intra-subject similarity was observed for left and right arms, suggesting that resistance to fatigue is more an individual ability than a motor skill differentiated for the dominant and non-dominant side. In conclusion, signs of a more selective neural recruitment, more coupled with muscular activity, appeared as short-term effects of muscular fatigue in primary sensorimotor cortical areas. Evidence suggested that the reduction of cortical recruitment and the increased cortico-muscular coupling are distinct mechanisms.