Kruk. В., Szczypaczewska M., Opaszowski В., Kaciuba Uściłko H., Nazar K. Thermoregulatory and metabolic responses to repeated bouts of prolonged cycle-ergometer exercise in man. Acta Physiol. Pol., Changes in body temperature, oxygen uptake (VO₂ ), heart rate (HR), sweating rate and plasma osmolality were examined in 10 human subjects, performing four successive 30 min exercise-bouts of the same intensity (50% VO₂ max) separated by 30 min rest periods. In spite of the rest intervals and replacement of body fluid loss there was a progressive increase in VO₂ . HR, rectal (Tre) and mean body (Tb) temperatures in consecutive exercise bouts. The thermoregulatory efficiency showed an increasing tendency, and a delay in the sweating response at the beginning of each exercise was shortened. It is concluded that a drift in metabolic and temperature responses to exercise, reported throughout a long-term continuous work, occurs also in the euhydrated subjects performing a prolonged intermittent exercise. It is not caused by an impaired thermoregulation during exercise but rather by insufficient restitution of metabolic processes during rest intervals.
Twelve male, sedentary volunteers (22.0 ± 0.7 yrs) were submitted to three weeks of a bicycle ergometer training, consisting of 45 min exercise (at 70% VO2max), 4 times in the first week and 3 times in the next 2 weeks. They performed four incremental exercise tests with the power output increased by 50 W every 3 min until volitional exhaustion: two before training (C1 and C2), and after one (T1) and three (T3) weeks of training. Before and after each load the plasma noradrenaline (NA), adrenaline (A) and blood lactate (LA) concentrations were determined in venous blood samples as well as plasma growth hormone (HGH) and cortisol concentrations before and at the end of exercise. A decrease in NA concentration was found already after 1 week of training at power output of 100 W (p<0.01) and 200 W (p<0.05). Similar decline was maintained after 3 weeks of training. No significant training-induced differences in plasma A concentration were found, however, the thresholds for both catecholamines were significantly shifted towards higher values after 3 weeks of training. One week of training caused a decrease in the pre-exercise (p<0.01), as well as post-exercise (p<0.05) plasma cortisol and HGH concentrations. It was concluded that endurance training induced a decrease in HGH, cortisol and NA concentration already after one week of training. A decline of pre-exercise plasma HGH and cortisol levels with time of experiment may, in part, indicate familiarization to exercise protocol.