Alleviating Heat Strain During Exercise: Hand Cooling and Thermoregulation

Exercise capacity and performance are impaired in hot and humid environments, principally due to an increased body temperature and cardiovascular strain. Strategies that alleviate heat strain and improve exercise capability are therefore meaningful from a safety and performance perspective. These strategies are often assessed using core body temperature as a primary outcome, usually derived from inside the rectum, but increasingly from the intestinal tract using gastrointestinal telemetry pill systems. The reliability of intestinal temperature, however, was unclear. Therefore, the purpose of study 1 was to investigate the inter-day reliability of intestinal temperature during an exercise-heat challenge. Gastrointestinal temperature demonstrated good reliability but researchers and practitioners should be aware of potential heteroscedasticity as the magnitude of error increases with temperature. This information is useful when examining the effectiveness of strategies to alleviate heat strain and improve performance. Indeed, there are many interventions designed for this purpose, however, few are practical enough to be used during continuous exercise in hot environments. The objective of study 2 was to systematically identify and meta-analyse the effect of practical cooling strategies applied during exercise in hot environments. Cooling during fixed-intensity exercise before a self-paced performance trial improves endurance performance in the heat. These improvements are most likely mediated by an improved rating of perceived exertion and heat strain but not by attenuating an increase in body temperature. A potentially effective site for limiting increases in body temperature during exercise is the hands. Therefore, the purpose of study 3 was to quantify the physiological and perceptual responses to hand immersion in water during recumbent cycling in a hot environment. Hand immersion in cold water attenuated an increase in body temperature compared to a thermoneutral control and elicited beneficial effects on heart rate, skin temperature and skin blood flow. The aim of study 4 was to extend these findings to investigate the effects of prototype cooling gloves worn during exercise in a hot environment. The cooling gloves decreased indices of intestinal and skin temperature as well as heart rate. Beneficial effects were also observed for rating of perceived exertion, thermal comfort and thermal sensation. The findings from these studies have practical implications for assessments of interventions using gastrointestinal temperature, the choice of practical cooling strategy used during exercise in the heat and the application of hand cooling strategies. Future research should aim to improve the ergonomics of the cooling gloves designed in study 4 and investigate their impact on exercise capability in hot environments.