Facial lower-region changes during high-intensity exercise as predictors of reduced arousal state

This study examined whether changes in facial muscle movements during incremental exercise testing are associated with mood indicators related to executive function. Twenty-five male university students performed incremental cycle ergometer test. Facial expressions were recorded and analysed using Py-Feat to detect action units (AUs), while heart rate, blood lactate concentration, rating of perceived exertion (RPE), and a Two-Dimensional Mood Scale were measured. Generalised additive mixed models were used to examine the relationships between 16 AUs and physiological/psychological indicators, and correlation analysis to assess AU changes across exercise intensity transitions. Exercise intensity-dependent changes were observed in numerous AUs, with AU10 (upper lip raiser), AU17 (chin raiser), AU25 (lips part), and AU26 (jaw drop) demonstrating strong correlations with exercise load, heart rate, blood lactate concentration, and RPE (r = 0.314-0.631, all p < 0.05). During transitioning from moderate-to-high intensity, AU25 changes were significantly negatively correlated with arousal changes (r = -0.436, p = 0.029). These findings found facial expression changes, particularly AU25, to be reliable indicators of physiological and psychological responses during exercise. They also support the inverted-U hypothesis of arousal and highlight facial expression analysis as a promising non-invasive tool for exercise monitoring and cognitive function optimisation.