Differential acclimatisation as a function of duration of exposure

Summary The length of time required to achieve the highest degree of acclimatisation was studied in two groups of men who were acclimatised at either one of two temperature conditions, namely 32.2 °/33.9 ° C W.B./D.B. or 33.9 °/35.5 ° C W.B./ D.B. The acclimatisation procedure consisted of 4 hours work daily at a metabolic rate of 5 kcal/min for the duration of 12 days. Changes in rectal temperature and heart rate followed immediately upon the first exposure to, and work in, heat. Judged by the rectal temperature reactions, the process of acclimatisation was completed within 8 days. An extension of the period of acclimatisation to between 9 and 12 days was without effect on the state of acclimatisation acquired by the subjects after an 8-day procedure. With an acclimatisation procedure shorter than 8 days the men were not fully acclimatised. Acclimatisation procedures of either 4, 5, or 6 days duration (at 32.2 ° C W.B.) induced a degree of acclimatisation in the subjects which proved to be adequate to enable them to work with body temperatures similar to those of fully acclimatised men, for periods of either 1, 2 or 3 hours respectively in the test environment.