Emotional states influence postural control, but previous studies have primarily focused on postural dynamics during quiet standing while viewing emotional pictures, using the center of pressure as a measure. However, the effects of emotions on neuromuscular activities related to postural control remain unclear. During quiet standing, neuromuscular activities of ankle plantarflexors are crucial for maintaining postural balance, both in terms of and synchronized muscle activity. 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 view emotional pictures for 72 seconds while standing. The task was repeated four times with four picture conditions, which 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 and 8–12 Hz. Results showed that aroused emotions induced a reduction in SOL neuromuscular activity, leading to partial backward body leaning. Furthermore, synchronized neuromuscular activities at 8–12 Hz in the SOL-MG and MG-LG pairs were increased under aroused emotional states, indicating enhanced physiological tremor and a reduced capacity for postural adjustment. These findings deepen our understanding of the emotional impacts on standing postural control.

Interoception, the internal perception of bodily states such as heartbeat and hunger, plays a crucial role in shaping cognitive and emotional states. Given that postural control affects cognitive and emotional processing, exploring postural effects on interoception could help uncover the neural mechanisms underlying its effects on cognition and emotion. In this study, we aimed to investigate how different postures affect interoception by using heartbeat-evoked potentials (HEPs), which are event-related potentials indicative of heartbeat processing in the cortex. The study included 21 healthy male participants. They were asked to sit in a chair (sitting condition) and stand (standing condition) in a relaxed state. Data from 64-channel electroencephalogram (EEG) and electrocardiogram (ECG) were collected. The EEG data were segmented by the R-wave timing detected from the ECG data for HEP analysis. HEPs were calculated by focusing on the 350–500 ms post-R-wave interval in the central and temporal brain regions. A paired t-test was performed to compare HEP amplitudes between the sitting and standing conditions, revealing significantly lower HEP amplitudes in the standing condition than those in the sitting condition (t=2.63, p=0.016, d=0.59). Furthermore, we explored the relationship between HEP changes and physiological changes such as cardiac activity and spontaneous EEG, finding no significant correlations (p>0.05, |r|<0.26). These findings suggest that the decreased HEP amplitudes observed during standing reflect attenuated interoceptive processing probably due to a redistribution of attentional resources from internal to external sensory processing, necessary for maintaining standing posture. Thus, postural differences may influence specific neurophysiological processes linked to interoception.