Effects of training and heat acclimatization on blood plasma contents of exercising men

Abstract

Five men trained 4 h/day for 43 days with increasing work loads on bicycle ergometers. Maximum O2 consumption (.ovrhdot.VO2 max) and lactate turn points (.ovrhdot.VO2 at which lactate production increases exponentially) were assessed before, during and after training. Following training the subjects were acclimatized to heat. A 4 h work test (stepping at 35 W) was done in a cool (18-22.degree. C) environment before training began, at intervals during training, and after acclimatization. The test was also repeated in a hot environment (33.8.degree. C db [dry bulb], 32.4.degree. C wb [wet bulb]) before and after training and acclimatization. During each test, mean skin temperature (.hivin.Tsk), rectal temperature (Tre), body weights, .ovrhdot.VO2, and blood samples were obtained. Training had little effect on thermoregulation during cool tests but did modify thermoregulatory mechanisms early in heat exposure. Work tests done in a cool environment were accompanied by hemoconcentration before and hemodilution after 3 wk of training. Protein dynamics and improvement in muscle metabolism contributed to the shift from hemoconcentration to hemodilution. Training stabilized plasma volume during a heat exposure but acclimatization afforded further protection against heat stress because of increased hemodilution and sensitivity of the sweat mechanism.