Sex differences in sympathetic and hemodynamic responses to exercise during heat exposure

Background: Exercise increases heart rate (HR), muscle sympathetic nerve activity (MSNA), and blood pressure (BP) through central command and the exercise pressor reflex (EPR). Prior work shows that whole-body heating (HT) attenuates the BP response to exercise without lowering MSNA responses. Studies also suggest sex differences in autonomic and hemodynamic responses, with women generally showing an attenuated pressor response. However, it is unclear whether HT affects the EPR differently in men and women. This study aims to determine sex differences in autonomic and hemodynamic responses to exercise under HT condition. We hypothesize that HT will produce a greater attenuation of pressor responses in women than in men. Methods: Total 36 healthy volunteers (58 ± 3 years; 20 M/16 F) performed static handgrip exercise to fatigue, followed by post-exercise circulatory occlusion (PECO) and passive muscle stretch during PECO, with the PECO and PECO + stretch conditions presented in random order. The protocol was completed under both normothermic (NT) and HT conditions during two separate, randomized visits. Whole body heating increased internal temperature by ~0.5°C using a water perfused suit, while the mean skin temperature was controlled at ~ 34°C in NT trial. MSNA, beat-to-beat BP (Finometer), and HR (ECG) were recorded continuously during each visit. Mean values from the final minute of handgrip and from each of the other stages of the exercise paradigm were used for comparisons. Results: Handgrip evoked significant increases in MSNA, HR, and mean arterial pressure (MAP) across all stages of the paradigm in both males and females under NT conditions. The HR responses (ΔHR, change from rest) at all stages of the paradigm were greater under HT than NT, with no sex-related differences observed. During handgrip, the ΔMAP in males did not differ between NT and HT, whereas females showed a significantly reduced ΔMAP in HT compared with NT (p < 0.001). Under HT, ΔMAP to handgrip was significantly lower in females compared to males (p < 0.001). Females showed a smaller ΔMSNA to handgrip than males (sex effect: p =0.023). During PECO, females had a smaller ΔMAP during PECO than males (sex effect: p = 0.038), and this difference persisted under HT (p = 0.045). The ΔMSNA during PECO did not differ by sex or thermal condition. During PECO + stretch, ΔMAP was lower in females than in males (sex effect: p = 0.009), and this difference persisted under HT (p = 0.004). No sex-related differences in MSNA responses were observed under this condition. Discussion and Conclusion: Our data show that whole-body heating attenuates pressor responses to exercise, even as HR responses are augmented, consistent with prior reports. This study demonstrates that the heat-induced attenuation of pressor responses is greater in females than in males. The smaller MSNA responses observed in females may contribute to this reduced pressor effect. Additionally, potential sex differences in heat-induced vasodilation and α-adrenergic receptor sensitivity may also play a role and warrant further investigation. Supported by NIH R01HL141198 and R01HL164571. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.