Menstrual cycle selectively elevates anticipatory effort cost without altering reward sensitivity in human motivation
Motivation fluctuates across the menstrual cycle, yet the computational mechanisms underlying these changes remain unclear. We tested whether hormonally defined cycle phases selectively alter distinct components of effort-based motivation in naturally cycling women (n=51), who completed an effort-reward decision-making task and an effort psychophysics task in both the late-follicular and mid-luteal phases, alongside electrocardiography and ecological momentary assessment. Hierarchical Bayesian modelling revealed that the anticipated cost of physical effort (effort sensitivity) was selectively elevated in the mid-luteal phase, with no corresponding change in reward sensitivity. The luteal increase in effort sensitivity was attenuated in women who entered that phase after days of higher affective valence and arousal, indicating that positive affective state buffers cyclical motivational vulnerability. Complementing these findings, phase-related individual differences in effort the mapping between objective and perceived effort (effort differentiation) were not different by phase, but were moderated by heart rate variability and momentary affective states, revealing stable person-level variation in how the cycle shapes effortful experience. Together, these results identify effort sensitivity as a specific computational mechanism of cyclical motivational change, with implications for understanding the elevated burden of cycle-related psychiatric conditions across the female reproductive lifespan.