Force-Temporal Characteristics of EEG-EMG Coherence During Isometric Contraction of the Tibialis Anterior Muscle

The coherence between electroencephalogram (EEG) and electromyogram (EMG) of the tibialis anterior (TA) muscle during isometric contraction is observed in the beta band (15 to 35 Hz). When the contraction force becomes stronger, the peak coherence frequency shifts to the gamma band (35 to 60 Hz). In contrast, based on the maintenance of contraction with the weak force, the peak coherence value increases. However, the manner in which coherence changes according to the maintenance of contraction with strong force remains unknown. In this study, five healthy male university students were directed to execute isometric contraction by dorsiflexion of their right ankle joint for 1 min with forces of 10 to 60% of the maximum voluntary contraction. During dorsiflexion, EEG and EMG of the TA muscle were performed. Then, the changes in coherence between EEG and EMG were examined, corresponding to the changes in contraction force and time course. In the majority of subjects, the peak coherence during the weak contraction force was observed in the beta band and lasted for 12 to 60 s. However, the peak coherence during the strong contraction force was observed in the gamma band only for the first 12 s. Subsequently, no significant coherence was observed. Therefore, muscle fatigue due to strong contraction forces and/or maintenance of the weak contraction force may have been observed as a different property of the peak coherence.