Objective: Cold exposure is common in work and recreation, yet most thermoregulation research has focused primarily on male responses. We used partitional calorimetry to compare thermoregulatory responses of males and females during graded passive cold exposure. Hypothesis: Based on previous literature, we hypothesized that sex would influence responses to cold, with females showing lower mean (Tsk) and index finger temperature, skin blood flow (LDF), and thermal comfort (TC), than men, but similar core temperature (Tre). Further, due to the predicted lower Tsk and body surface area in females, we expected females to have lower required (Mreq) and actual (Mact) metabolic rates to maintain heat balance. Methods: Following institutional review board approval, eleven participants (6 males: 28±10 y, 81.1±8.0 kg, 1.81±0.3 m; 5 females: 21± 2 y, 73.2±13.9kg, 1.6±0.09 m) ate a standardized breakfast, donned athletic shorts (and sports bras for females), and were instrumented, then seated in an environmental chamber initially set at 22°C, 50% relative humidity, and air speed of 2 m·s - ¹. Ambient temperature decreased by 6°C every 30 min (22, 16, 10, 4°C). Tre, 10-site weighted Tsk, trapezius LDF, and expired gases (breath-by-breath) were measured continuously; TC and digit (index finger) temperature were recorded every 5 min. Mreq was calculated from partitional calorimetry equations using Tsk, ambient conditions, air velocity, and body surface area. Mact was derived from expired gases using indirect calorimetry. Both Mreq and Mact are reported in watts (W). All data are presented as means ± standard deviation. Results: No differences in Mreq between sexes were observed at any temperature (22°C: 137±24 W, 16°C: 187±29 W, 10°C: 233±36 W, 4°C: 284±41 W; all p>0.614). Mact was not different between sexes at 22°C (126±21 W, p=0.421) and 16°C (151±34 W, p=0.179), but was greater in males at 10°C (M: 254±65 W, F: 183±28W, p=0.044) and 4°C (M: 353±64 W, F: 244±14 W, p=0.008). In comparing Mreq to Mact within sex, males did not differ at any air temperature (22°C: p=0.688; 16°C: p=0.142; 10°C: p=0.609; 4°C: p=0.061); however, in females, Mact was lower than Mreq at 16°C (p=0.033) and 10°C (p=0.041), but not 22°C (p=0.293) and 4°C (p=0.146). Tre was similar between sexes and did not meaningfully decrease with lowering air temperatures (22°C: 37.2±0.4°C, p=0.148, 4°C: 37.0±0.5°C, p=0.135). Tsk was similar between sexes across all air temperatures (22°C: 28.9±1.1°C, 16°C: 25.5±1.4°C, 10°C: 21.8±1.6°C, 4°C: 18.2±1.8°C; all p>0.678). No differences in LDF between sexes were observed at any air temperature (22°C: 27±5 AU, 16°C: 24±5 AU, 10°C: 20±5 AU, 4°C: 17±6 AU; all p>0.632). TC was equivalent between sexes at all air temperatures (22°C: -0.5±0.7 AU, 16°C: -1.6±1.3 AU, 10°C: -2.0±1.7 AU, 4°C: -2.2±1.8 AU; all p >0.706). Finally, digit temperature was similar between sexes across all air temperatures (22°C: 24.2±1.3°C, 16°C: 21.5±2.4°C, 10°C: 17.3±2.4°C, 4°C: 12.5±2.4°C, all p>0.545). Conclusion: Statement Biological sex had minimal influence on thermoregulatory responses to graded cold stress. Males exhibited higher metabolic heat production than females at the coldest air temperatures (10 and 6°C), while female’s Mact fell below predicted Mreq without producing detectable differences in core or skin temperature over the duration of this protocol. Funding This study was funded by the PI’s start-up funds. 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.
Ries et al. (Fri,) studied this question.