This paper reports a research conducted to determine the changes in the electrical activity of the contralateral motor cortex of the brain that drives the maximum voluntary contraction (MVC) of right Adductor Pollicis muscle (APM) after fatigue. For this aim, the power changes of EEG signals after muscle fatigue were computed. EEG signals from the left motor cortical area (C3, FC3) in twenty-five subjects, simultaneously with the EMG from right Adductor Pollicis muscle (APM), before and after exercise-induced fatigue were recorded. The Root Mean Square (RMS) of the EEG bands (alpha, beta, and gamma) was calculated to determine the power changes of the EEG signals after right APM fatigue. The mean RMS of EEG bands were increased during MVC of fatigued right APM compared to the RMS value during relaxation before fatigue (p<0.05). The RMS value was seen to be greatest in the beta band, and lowest in the gamma band. The observed increase in the RMS of EEG bands during MVC of fatigued right APM suggest an increase in the EEG signals power, which could reflect an increase in energy needed by the motor cortex to perform MVC in fatigued muscle, which might give an indication of neural fatigue in the motor cortex.

It is known that movements of the right side of the body are controlled by the left motor cortex of the brain. The aim of this study is to evaluate the contribution of right motor cortex of the brain in the central motor control of right-sided muscle contraction. EEG/EEG coherence analysis has been used to determine the functional coupling between the right and left motor cortical areas in twenty normal volunteers, during maximum voluntary contraction (MVC) and 50% MVC of right Adductor Pollicis muscle (APM). It shows that the maximum mean coherence values were: 0.751 during MVC at 10 and 12 Hz, and 0.274 during 50% of MVC at 22 Hz. The minimum mean coherence values were: 0.716 during MVC at 48 and 50 Hz, and 0.242 during 50% MVC at 34 Hz. The high coherence values obtained during MVC, and to a lesser extent during 50% of MVC, could be attributed to the need of recruitment of both motor cortical areas during the decision phase of central motor control of voluntary muscular contraction. The "will" to perform maximum voluntary contraction could be a major factor, which contribute to the higher coherence values obtained during MVC than these associated with 50% of MVC.