COOLING DEVICES WORK BETTER OVER ACTIVE MUSCLE THAN OVER INACTIVE MUSCLE

DeGroot, D. W., Cheuvront, S. N., Kolka, M. A., Cadarette, B. S., Montain, S.J., & Sawka, M. N. (2004). Intermittent regional microclimate cooling over active vs. non-active muscle. Medicine and Science in Sports and Exercise, 36(5), Supplement abstract 2135.

Previous research has indicated that micro-climate cooling (MCC) over active muscle is more effective (greater core-to-skin gradient without evoking a reflex vasoconstriction) than over non-active muscle. Additionally, intermittent regional micro-climate cooling (IRC) has been shown to be as effective as constant cooling, while providing a potential engineering advantage through reduced power requirements. The effect of IRC over active vs. non-active muscle has not been examined (p. S313). This study examined if IRC over active muscles would be more effective than over non-active muscles. Heat-acclimated men (N = 5) performed a 75-minute treadmill walk in a warm climate (30C) while wearing chemical protective clothing with a water-perfused (21C inlet temperature) cooling undergarment. Cooling water flow was supplied 1-minute-on/3-minute-off, with only one region cooled (thigh and calf vs. chest and upper back) at any time. Flow rates to different regions were adjusted to yield a theoretical heat removal potential of 6W/unit body surface area.

Skin temperature over active muscle was 1.2C cooler than skin temperature over non-active muscle (3.66 and 2.46C less than core temperature, respectively). Area-under-the-curve for active muscle skin temperature was less than non-active muscle skin temperature. Cooling over active muscle was more effective at keeping skin temperature in the range for optimal heat transfer.

Implication. Intermittent regional micro-climate cooling is more effective (greater core-skin temperature gradient) over active muscles compared to non-active muscles. Additionally, cooling over active muscles maintained skin temperature in the optimal range of 33-35C better than cooling over non-active muscle.

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