INTERMITTENT-REGIONAL MICROCLIMATE COOLING REDUCES EXERCISE-HEAT STRAIN MORE EFFICIENTLY THAN CONSTANT COOLING PARADIGMS

Abstract

The vasomotor response to cold can decrease skin heat flux and compromise the capacity for microclimate cooling (MCC) to reduce thermoregulatory strain. PURPOSE This study examined the hypothesis that intermittent-regional microclimate cooling (IRC) would 1) reduce exercise-heat strain comparably to constant microclimate cooling (CC), and 2) improve microclimate cooling efficiency by intermittent perfusion of a small body surface area (BSA), thus increasing regional skin heat flux when compared to the constant perfusion of coolant over a larger BSA. The efficacy of four different IRC regimens was compared. METHODS Five heat-acclimated men performed six experimental trials of treadmill walking (225 W• m−2) in a warm climate (Tdb = 30° C, Tdp=11° C) while wearing chemical protective clothing (clo = 2.1; im = 0.32) with a water-perfused (21° C) cooling undergarment. The six trials conducted were: CC of 72% BSA, two IRC regimens cooling 36% BSA (with 2:2 or 4:4 min on: off perfusion ratios), two IRC regimens cooling 18% BSA (with 1:3 and 2:6 min on: off perfusion ratios), and a no cooling (NC) control. RESULTS Compared to NC, CC significantly reduced Δ Tre (1.2° C) and Δ HR (60 b• min−1) (P < 0.05). The four IRC regimens all provided a similar reduction in exercise-heat strain and were 164 – 215% more efficient than CC due to improved heat flux over a smaller BSA. CONCLUSION These findings indicate that the IRC approach to MCC is equally effective in reducing exercise-heat strain and may reduce MCC power requirements by providing a more efficient means of cooling when compared with CC paradigms.