Hand and forearm cooling: Exploring deep-body cooling in hyperthermic individuals following exercise-induced heating at three different work rates

The purpose of this study was to evaluate upper-limb cooling following (treadmill) exercise performed in the heat (33(o)C, 70% relative humidity) at each of three speeds: light (6 km.h(-1)), intermediate (8 km.h(-1)) and moderate intensity (10 km.h(-1)). In all trials, exercise ceased when rectal temperature reached 39.0(o)C. Participants adopted a sitting position for a 20-min recovery, and liquid-cooling sleeves with cold water (6.3(o)C) were immediately positioned. The chosen work rates resulted in a two-fold difference in exercise duration across those trials, which terminated without significant between-trial differences within either auditory canal or rectal temperatures. Auditory canal temperature elevation rates became progressively faster as the work rate increased: 0.03(o)C.min(-1) (light), 0.05(o)C.min(-1) (intermediate) and 0.07(o)C.min(-1) (moderate) (p<0.05). However, heat extraction during recovery did not differ among those treatments: -11.2 W (SE 0.5; light), -11.8 W (0.6; intermediate) and -12.3 W (0.5; moderate; p>0.05). That outcome was reflected in auditory canal cooling rates (0.03(o)C.min(-1) [light], 0.04(o)C.min(-1) [intermediate] and 0.05(o)C.min(-1) [moderate]). Nevertheless, rectal temperatures continued to rise throughout recovery. It is concluded that heat extraction from moderately hyperthermic individuals, using upper-limb cooling sleeves, appears to be equally rapid, regardless of heating speed, providing the same level of hyperthermia was attained prior to initiating treatment.