<p>This study examined modulations of the cardiac autonomic nervous system, neuromuscular performance and psychological states during the menstrual cycle (MC) in naturally menstruating women. Fifteen healthy young females were tested during menstruation, estimated late follicular, and estimated mid-luteal phases. Each session included mood and motivation assessments, resting heart rate variability (HRV) analysis and a maximal voluntary isometric contraction test of the knee extensors. Our data revealed a significant decrease of the parasympathetic activity reflected by lower vagally derived HRV indices (root mean square of successive R-R interval differences and high frequency spectral component) during the mid-luteal phase compared to both menstruation and late follicular phases. However, no significant difference was detected for maximal force, rate of force development (RFD), and associated electromyographic activity (EMG). Among psychological variables, the Depression subscale score was the only one that increased during the late follicular phase. No significant correlations were observed between most HRV indices, neuromuscular performance variables, and psychological measures. However, perceived Vigour was positively associated with EMG activity during the RFD phase. In addition, autonomic balance was related to RFD, with low frequency (nu) positively and high frequency (nu) negatively correlated with explosive force production. These findings suggest cardiovagal modulation across the MC. HRV appears to be a sensitive physiological marker of menstrual-related autonomic shifts, with potential implications for monitoring female athletes.</p>