ARMSTRONG, L. E., R. W. HUBBARD, J. P. DELUCA, and E. L. CHRISTENSEN. Heat acclimatization during summer running in the northeastern United States. Med. Sci. Sports Exerc, Vol. 19, No. 2, pp. 131-136, 1987. Five highly trained distance mnners(DR) were observed during controlled 90-min thermoregulation trials in spring (T1) and late summer (T2) to document the nature of heat acclimatization in the northeastern United States. These trials simulated environmental (30.3 +/- 0.1[degrees]C dry bulb, 34.9 +/- 0.5% relative humidity, 4.47 m[middle dot]s-1 wind speed) and exercise (treadmill running at 80, 120, 160, and 200 m[middle dot]min-1) stresses encountered by DR during summer training in the northeastern United States. Between T1 and T2, DR trained outdoors for 14.5 +/- 0.4 wk, but consequently exhibited few physiological adaptations classically associated with heat acclimatization. Statistical comparison of T1 and T2 indicated no significant differences in mean heart rate, rectal temperature, sweat Na+ and K+, plasma Na+ and K+, or change in plasma volume during exercise. Mean weighted skin temperature was unchanged except at 50 min of exercise, and sweat rate was also unchanged except during the initial 30 min segment: 73 +/- 6 vs 93 +/- 8 ml[middle dot]m-2[middle dot]h-1. Significant decreases (P < 0.05) in submaximal [latin capital V with dot above]O2 were observed: T1 vs T2 values were 13.97 +/- 0.27 vs 10.19 +/- 1.19, 31.38 +/- 1.15 vs 27.91 +/- 1.45, and 44.97 +/- 0.85 vs 41.24 +/- 0.97 ml[middle dot]kg-1[middle dot]min-1, at treadmill speeds of 80, 120, and 200 m[middle dot]min-1, respectively. We conclude that DR did not require 14.5 wk of summer training to maintain safe rectal temperatures (<=38.4[degrees]C) during T1, which simulated the hottest days of summer in the northeastern United States.
(C)1987The American College of Sports Medicine