Strenuous Exercise in a Hot Environment

¹ From the Sir William MacGregor School of Physiology, University of Queensland, Brisbane, Australia

Oarsmen worked at a rate of 0.58 h.p. for 6 minutes on a rowing ergometer in a psychrometric chamber at 80° and 112°F. Diastolic pressure immediately after the cessation of exercise was zero, while the average systolic pressure was 185 mm Hg. The pulse rate was 144–208/min. within 1 minute after exercise. The average increase in hematocrit was 12%. A large loss of plasma water, 0.6–1.9 liters, was more than sufficient to account for the increase in hematocrit and was considered to contribute to the tachycardia and low diastolic pressures. The hotter conditions did not affect the performance nor the amount of fluid redistribution. The recovery period at 112°F, however, was characterized by circulatory embarrassment in five of eight cases. Low blood pressures persisted and were accompanied by higher pulse and respiratory rates than those observed during recovery at 80°F. Excretion of 17-OH-steroids was higher when there had been distress.