Blunted baroreflex-mediated sympathoinhibition and vasodilation to countdown before exercise in young women compared to men.

Purpose: In our previous study (Manabe et al., J Appl Physiol 128:1196-1206, 1985), we demonstrated that the cerebral and cardiovascular responses induced by a pre-exercise countdown elicited peripheral vasodilation via baroreflex-mediated sympathetic withdrawal, which is likely advantageous for rapid oxygen delivery to contracting skeletal muscles in young men. Whether this is also true in young women, who generally show different neuro-cardiovascular responses to stress compared to men, remains unknown. Thus, we examined whether biological sex would affect the neuro-cardiovascular responses to anticipation before exercise.

Methods: Young healthy women (n = 11) and men (n = 10) performed 1 min of static handgrip at 30% of maximal voluntary contraction force twice; once with a 30 sec countdown and once after being immediately signaled to begin exercise (without countdown), with the order randomized. Middle cerebral artery blood velocity (V_MCA; transcranial Doppler), heart rate (HR), cardiac index [CI; HR × stroke volume (Modelflow)/body surface area], mean arterial pressure (MAP; finger photoplethysmography), muscle sympathetic nerve activity (MSNA; microneurography), and leg vascular conductance [LVC = superficial femoral artery blood flow (ultrasound)/MAP] were measured continuously.

Results: During countdown, women exhibited smaller increases in CI, MAP, and LVC and a smaller decrease in MSNA than men (p < 0.05). Increases in V_MCA and HR, and the sympathetic baroreflex sensitivity did not differ between sexes (p > 0.05).

Conclusion: Young women seem to have less baroreflex-mediated sympathetic withdrawal and peripheral vasodilatory responses to the countdown compared to young men, despite similar cerebral vascular responses. These findings may suggest women have reduced neuro-vascular responses to exercise anticipation, which could impact the ability of oxygen delivery at exercise onset.