Physiological acclimatization to heat after a spell of cold conditioning in tropical subjects.

The effects of brief spells of cold conditioning on heat acclimatized tropical subjects on the decay and reacclimatization status to heat were evaluated on 12 Indian male infantry soldiers in the cooler months at Delhi. After 8 d of heat acclimatization in a climatic chamber maintained at 45 degrees C dry bulb (Tdb) and 30% relative humidity (rh), the subjects were conditioned to cold for 21 d by exposing them to a temperature of 10 degrees C daily for 4 h. During the cold conditioning phase the subjects had no access to either heat exposure or strenuous work. The cold conditioning was followed by reacclimatization to heat. Significant loss in heat acclimatization status was observed, both in terms of exercise oral temperature and heart rate. The loss in status after 1 d reinduction to heat acclimatization was in the range of 45-56%. However, within 3 d all of the subjects once again regained the full acclimatization status. The cold conditioning did not alter the sweat output during the reinduction to heat phase.