Effect Of Dry And Wet Heat Acclimation Strategies On Exercise Endurance During Warm Water Dives

Abstract

Diving in warm water imposes greater thermal risk to Navy divers during exercise compared to thermoneutral waters. Heat acclimation strategies to reduce thermal load of warm water diving have rarely been examined. PURPOSE: Evaluate diver exercise endurance in warm and hot water conditions after wet and dry heat acclimation. METHODS: Twenty male divers completed this study at the Navy Experimental Diving Unit. Subject pairs were matched by VO2max and randomly assigned to one of two heat acclimation groups. One group (n = 9) cycled at 125-150 W for one hour in a non-immersed (DRY) condition (34.4 °C, 50% relative humidity) while the second group (n = 11) cycled at 50 W for one hour while immersed in 34.4 °C water (WET). Following ten days of acclimation, diver endurance was tested via exercise time to exhaustion on an underwater cycle ergometer in 35.8 °C (WARM) and 37.2 °C (HOT) water at a fixed intensity of 50 W on separate days. Core temperature (Tc) was continuously recorded and for all dives, subjects wore light “dive skins” used by Special Operations Forces (SOF) divers. Data was analyzed with two-way analysis of variance compared between water temperatures and acclimation groups. RESULTS: Time to exhaustion was reduced in WARM compared to HOT water (p < 0.01) in both DRY (92.7 ± 41.6 min in 35.8 °C vs. 43.4 ± 17.5 min in 37.2 °C) and WET (98.7 ± 38.4 min in 35.8 °C vs. 51.7 ± 26.7 min in 37.2 °C) groups, but did not differ between groups (p = 0.53). Rate of Tc rise was greater with higher water temperature (main effect: p < 0.01) but was not different between DRY and WET groups (p = 0.74). Maximum Tc (p = 0.74 and p = 0.95) and Tc change from baseline (p = 0.95 and p = 0.56) was not different between water temperatures or acclimations group, respectively. CONCLUSIONS: Diver endurance decreased with increased water temperature but was unchanged between WET and DRY heat acclimation. Divers became exhausted at a similar core temperature during WARM and HOT water exercise. Mechanisms and applications of heat acclimation for warm water diving should be further explored. The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of the Army, Department of Navy, Department of Defense, or the U.S. Government.