Thermoregulatory Sweating during Cold Transients and Exercise: Effect of Menstrual Cycle phase

Abstract

Thermoregulatory sweating during light exercise during cold air temperature transients was examined in women at two different phases of their menstrual cycle. Nine women with normal menstrual cycles participated (age=27.2±4.5 y; DuBois Surface Area=1.6±0.1 m²; % Body Fat=20.0±3.8%; heart rate maximum=195±6.1 beats·min⁻¹, and VO_2,max=46.2±4.4 mL·kg⁻¹ min⁻¹). Experiments were conducted in the late fall, winter, and early spring at the same time of day (0700–0900 h). The women were studied in their early follicular (F) and mid-luteal (L) phases clothed in fatigues+Goretex^TM parka during treadmill exercise (∼34% VO_2,max). Air temperature (T_a) was decreased from an initial level of 20°C/40% RH to −5.0°C (wind speed of 1 m·s⁻¹) at a rate of −0.3°C·min⁻¹ over 80 min. Esophageal (T_es), mean skin (T_sk) and upper arm (T_arm) temperatures, VO₂, and arm sweating rate (m_sw) were recorded continuously. For the first 40 min of exercise, m_sw was correlated with T_es (r²=0.66 in F and 0.75 in L) but became inhibited by cold T_sk during the final 40 min. Throughout the exercise/cold transient, m_sw was higher (P<0.05) and T_es threshold temperature was increased by 0.35°C in the L vs F. Sudomotor control was adequately predicted using a maximum likelihood estimation model combining T_es, T_sk and T_arm. The model confirmed that the m_sw is a function of T_es, T_sk & T_arm, increases by 22% (P<0.05) as T_es threshold is displaced upwards in the L phase. In conclusion, sweating rates in the F and L during light exercise are influenced separately by changes in skin cooling and may be highly responsive to perturbations in hormonal balance.