King's College London
The effect of head cooling on cardiovascular and thermal responses
to exercise in the heat.
Richard Massey
This study evaluated the effects of a liquid conditioned hood on the cardiovascular and thermal responses to a brief work/rest protocol in a hot environment. The chamber was set at dry bulb temperature 40°C, wet bulb temperature 30°C and relative humidity 40 %. The hood was made of stretch nylon with approximately 17 m of PVC tubing (inside diameter 2 mm, outside diameter 2.5 mm) sewn onto the inner surface (The hood was kindly loaned by the Centre for Human Sciences - Qinetiq). Water flow through the hood was set at 0.8 L/min via a 24V liquid pump and the water temperature was maintained at 8-11°C using a refrigerated cooler unit and a heating unit with a thermostat. The volunteer subjects who were six healthy men participated in two 80 minute work/rest trials. The protocol was divided into 10 min exercise on a cycle ergometer with an external load of 150 W followed by 10 min rest - repeated 3 times with a final recovery period of 30 min. In one trial subjects had their head cooled during each rest period (COOL) and in a second trial no cooling was provided (CONT). Cooling effects were evaluated by recording tympanic temperature, mean skin temperature, scalp temperature, heart rate, forearm blood flow, sweat rate and a subjective comfort assessment.
Head cooling during rest periods caused a reduction in tympanic temperature, scalp temperature and heart rate which continued into subsequent exercise periods. The recovery of heart rate during each rest period was more rapid in COOL. Mean skin temperature was not affected by cooling at all. Subjective ratings of head, body and overall thermal comfort at the beginning and end of each rest period were improved by head cooling. Forearm blood flow was measured at the beginning and end of each rest period and was also significantly reduced by head cooling. Overall sweat rate was reduced by 30% in the COOL condition. These results suggest that, when used during rest periods between brief work/rest cycles in the heat, head cooling both enhances recovery and attenuates the cardiovascular and thermal responses to subsequent exercise. Benefits of head cooling during brief work/rest cycles in a hot environment include a reduced sweat rate, lower heart rate and improved thermal comfort.
This project was supervised by Professor J. Ernsting and was submitted for the degree of MSc Human and Applied Physiology 2002
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