Jonkman, A. G., Linnane, D. M., Weller, A. S., & Daanen, H. A. (2007). Acclimation to moderate heat adequately prepares individuals for work in a hotter environment. ACSM Annual Meeting New Orleans, Presentation Number 1839.

This study established whether heat acclimatization in a moderately hot environment (would prepare individuals to undertake moderate exercise in a hotter environment. Males (N = 15) exercised on a cycle ergometer for up to two hours per day on 12 consecutive days in a hot chamber. For the first nine days the temperature was 26ºC and 32ºC during the last 3 days. Rectal temperature, heart rate, mean skin temperature, and sweat rate were measured during the first 60 minutes of steady state exercise (~45% of VO2max). Thereafter, the tolerance time was measured during graded cycle exercise to volitional fatigue.

Rectal temperature, heart rate, and skin temperature reduced to a plateau during the lower temperature. Tolerance time increased to a plateau. Sweat rate did not change. During the higher temperature days, rectal temperature, heart rate, and skin temperature increased significantly, whereas tolerance time decreased when compared to the last day of the lower temperature. However, there were no significant changes for any of the parameters within the three days in the hotter environment.

Implication. Moderate exercise performed at a 26ºC for approximately two hours per day on nine consecutive days developed full heat acclimatization. No further physiological adaptations were observed when the same exercise was undertaken at 32ºC over three days. Individuals may be adequately prepared for working in a hotter environment by prior heat acclimatization in a moderately hot environment.

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