Modulation of individual and synchronized activities of ankle plantarflexors during quiet standing in aroused emotions.

Emotions influence postural control, but previous studies have mainly examined postural dynamics during quiet standing using the center of pressure as a measure. During quiet standing, neuromuscular activities of ankle plantarflexors are crucial for maintaining postural balance, both in terms of individual and synchronized activities. This study aimed to clarify the emotional effects on the individual and synchronized neuromuscular activities of ankle plantarflexors during quiet standing. Twenty-four healthy male participants were instructed to stand and view emotional pictures for 72 s following a fixation cross. The task was repeated four times with four picture conditions, which was composed of two arousals (High and Low) and two valences (Pleasant and Unpleasant). During the task, electromyograms (EMG) of the tibialis anterior (TA), soleus (SOL), and medial (MG) and lateral gastrocnemius muscles (LG) were recorded. The EMG signals were rectified, and mean amplitude was calculated to assess individual neuromuscular activity. Inter-muscular coherence (IMC) between ankle plantarflexors was calculated to assess synchronized neuromuscular activity, with mean IMC calculated at 0-4 Hz, 8-12 Hz, 15-30 Hz, and 30-40 Hz. Results showed that aroused emotions induced a reduction in SOL activity. Aroused emotions also increased IMC at 8-12 Hz, indicating enhanced physiological tremor and reduced capacity for postural adjustment. In addition, IMC at 15-30 Hz was increased while 30-40 Hz was decreased in aroused emotions, implying modulation of cortical common drive to ankle plantarflexors.These findings deepen our understanding of the emotional impacts on standing postural control.