Influence of prolonged continuous exercise on hormone responses to subsequent exercise in humans

This study examined the possibility that fatigue may modify the hormone res ponses to exercise. A group of 12 endurance trained athletes ran for 2 h (b lood lactate concentrations of approximately 2 mmol.l(-1)) in order to indu ce fatigue. The subjects exercised for 10 min at 70% maximal oxygen uptake before (Ist test) and after (2nd test) the 2 h run to assess hormone respon siveness. A I min anaerobic power test was performed to assess muscle power . Cortisol, growth hormone, testosterone and insulin concentrations were de termined before and after the Ist and 2nd tests. The I st test resulted in increases in concentrations (P < 0.05) of cortisol and growth hormone, a de crease in insulin concentration (P < 0.01) and no change in testosterone co ncentration. The 2 h run caused decreases of insulin, increases of growth h ormone concentration and variable responses in the concentrations of cortis ol and testosterone. The 2nd test decreased insulin concentration further ( P < 0.05), but responses of the concentrations of testosterone, growth horm one and cortisol were variable. In 6 subjects (group A) cortisol displayed an increase [mean (SD)] from baseline concentrations [ + 304.0 (60.0) nmol. l(-1)], while in the other 6 subjects (group B) a decrease or no change was seen [+3.1 (5.3) nmol.l(-1), between groups, P <0.051. Growth hormone conc entration was substantially higher in group A [ + 14.7 (4.8) ng.ml(-1)] tha n group B [ + 6.0 (2.9) ng.ml(-1)] following the 2nd test. In group A anaer obic muscle power was higher, while in group B it was lower, after the 2 h run than before the 2 h run (P < 0.05). The findings suggest that fatigue f rom prolonged endurance activity may introduce a resetting in the pituitary -adrenocortical component of the endocrine system, expressed either by inte nsified or by suppressed endocrine functions.