Female (Under) Representation in Exercise Thermoregulation Research

Background Despite an increasing rate of women participating in professional sports, emergency services, and military settings where they are exposed to exertional heat stress, our understanding of female thermoregulation and the detrimental effects of heat on women’s performance, especially regarding the menstrual cycle, is limited. This review aimed to quantify the representation of women in exercise thermoregulation research between 2010 and 2019 and the frequency that these articles reported details pertaining to female participants’ menstrual cycle to determine the volume of novel research that is directly relevant to this growing population. Methods Original exercise thermoregulatory studies published in three major sports medicine databases (PubMed, MEDLINE, and SPORTDiscus) between 2010 and 2019 were surveyed. Articles were screened to determine the number of female and male participants in the study and whether studies involving women reported menstrual orientation or phase. Research involving healthy adult participants and an exercise protocol with a thermoregulatory outcome measure were included in the review. Results A total of 1407 articles were included in the review, involving 28,030 participants. The annual representation of women ranged from a mean of 11.6% [95% credible interval (CI); 9.2, 14.3] to 17.8% [95% CI; 15.2, 20.6] across the 10 years, indicating studies predominantly included men. Nonetheless, there was a small statistical increase in the overall proportion of women, with a mean overall proportion change of 0.7% [95% CI; 0.2, 1.2] per year. The increase appeared to be driven by a reduction in the number of studies including only men, rather than studies including more women alongside men, or increased women-only studies. Less than one third of articles involving women reported the menstrual orientation of participants and less than one quarter reported both menstrual orientation and phase. Summary/Conclusion This study shows that women were proportionally underrepresented in exercise thermoregulation research during the past decade and the majority of studies did not report menstrual cycle details of female participants. Researchers should consider including women in future work where their inclusion could contribute meaningful data that enhance the evidence-based and ultimately improves our comprehension of women’s thermal physiology.

Role of skin blood flow and sweating rate in exercise thermoregulation after bed rest

Two potential mechanisms, reduced skin blood flow (SBF) and sweating rate (SR), may be responsible for elevated intestinal temperature (Tin) during exercise after bed rest and spaceflight. Seven men underwent 13 days of 6° head-down bed rest. Pre- and post-bed rest, subjects completed supine submaximal cycle ergometry (20 min at 40% and 20 min at 65% of pre-bed rest supine peak exercise capacity) in a thermoneutral room. After bed rest, Tin was elevated at rest (+0.31 ± 0.12°C) and at the end of exercise (+0.33 ± 0.07°C). Percent increase in SBF during exercise was less after bed rest (211 ± 53 vs. 96 ± 31%; P ≤ 0.05), SBF/Tin threshold was greater (37.09 ± 0.16 vs. 37.33 ± 0.13°C; P ≤ 0.05), and slope of SBF/Tin tended to be reduced (536 ± 184 vs. 201 ± 46%/°C; P = 0.08). SR/Tin threshold was delayed (37.06 ± 0.11 vs. 37.34 ± 0.06°C; P ≤ 0.05), but the slope of SR/Tin(3.45 ± 1.22 vs. 2.58 ± 0.71 mg · min−1 · cm−2 · °C−1) and total sweat loss (0.42 ± 0.06 vs. 0.44 ± 0.08 kg) were not changed. The higher resting and exercise Tin and delayed onset of SBF and SR suggest a centrally mediated elevation in the thermoregulatory set point during bed rest exposure.