Relationship between body surface cooling area, cooling capacity, and thermoregulatory responses wearing water purfused suits during exercise in humans

Abstract

This study analyzed the effects of various body surface areas being cooled by water-perfused suits (WPS) on thermoregulatory response during exercise in a hot environment. Seven male subjects, dressed in clothing with low moisture permeability (rain coats) over WPS covering the whole body surface except for the face, hands, and feet, performed three sessions of 20-min cycling at low intensity (250w/m2) in a room maintained at 30°C under six conditions of body surface cooling: whole body (WB), upper body (UB), lower body (LB), lower body except lower legs (LBEL), head and neck (HN), and no body cooling (NBC). The coolant temperature at the inlet was 20°C for all conditions, and heat extraction (HE) was estimated by the difference between inlet and outlet water temperatures and water flow rate. Esophageal (Tes) and deep thigh temperatures (T-d.thigh) and heart rate (HR) during exercise were significantly (p<0.01) higher for NBC and HN, and forearm skin blood flow (SkBF) and dehydration (DEH) were significantly (p<0.01) lower for WB than for other conditions. There was a similar tendency concerning Tes and T-d.thigh among WB, LBEL, and LB; however, T-d.thigh for UB was significantly (p<0.01) higher than for WB, LBEL, and LB. In comparison with resting levels, the mean skin temperature (Tsk) and thermal sensation (TS) significantly (p<0.01) increased for NBC and HN, and decreased for UB and WB, but remained constant for LBEL and LB during exercise. Under all conditions, increases in Tes (ΔTes) and T-d.thigh (ΔT-d.thigh) at the end of exercise were significantly (p<0.01) increased when less than 40% of the body surface was cooled (T̄sk: above 35.8°C, HE: less than 110W). Furthermore, ΔTes at the end of the exercise was related to Δ Tsk × SkBF, while the slope of the regression line between those parameters was steeper when ΔT̄sk×SkBF values were negative, as opposed to posi-tive values. These results suggest that during light exercise under different body surface cooling conditions : 1) UB leads to a high T-d.thigh while Tes, Tsk, and TS are as low as those for WB, 2) critical levels of body surface cooling area causing a decrease in core temperature elevation might exist, and 3) changes in blood circulation due to body cooling might be affecting temperature responses at the end of exercise.