PURPOSE: Stress-related psychiatric disorders (such as depression) are twice as common in women as in men and have been linked to aberrations in physiological and psychological stress responding. Being physically fit may be protective against the development of adverse symptoms related to stress, however, to date, there has been limited investigation of the relationship between physical fitness and behavioral and physiological responses to stress which considers the profound influence of the ovarian cycle on physiological and behavioral stress responding. This study aims to investigate the relationship between physical fitness and physiological and behavioral (sleep disturbances) responses to stress in women during the follicular phase of the menstrual cycle (when ovarian hormones are low and stable). METHODS: Following a two-tiered screening process, 10 healthy women (18-45y) who were medication-free and had regular menstrual cycles were enrolled. Participants completed: (1) enrollment visit, (including mood and sleep assessment and assessment of cardiorespiratory fitness via maximal oxygen consumption during exercise); (2) one-week sleep monitoring period (objective and subjective measures of sleep-wake behavior); and (3) psychosocial stressor protocol for the collection of hemodynamic [blood pressure (SBP, DBP) and heart rate (HR)] and hormonal stress responses. Psychosocial stress testing sessions occurred during the follicular phase of the menstrual cycle to control for hormone fluctuations which can influence the physiological response to stress. RESULTS: Though not significant at this time, preliminary results from this ongoing study show that higher levels of physical fitness may be associated with lower sleep reactivity to stress (r = -.43, p = 0.17) and reduced wake after sleep onset (WASO; r = -.58, p = .07). Consequently, increased WASO was significantly associated with increased SBP and DBP reactivity to an acute psychosocial stressor (r’s = .78, .65; p’s = .01, .05 respectively). CONCLUSIONS: If confirmed in our larger sample results suggest that, in women, physical fitness may be protective against the physiological response to stress, perhaps via reduction in stress-related sleep disturbances.