Effect of restricted blood flow on exercise-induced hormone changes in healthy men.

To test the influence of the accumulation of metabolites on exercise-induced hormone responses, plasma concentrations of cortisol, growth hormone (GH), insulin, testosterone, thyrotropin (TSH), free thyroxine (fT4) and triiodothyronine (T3) were compared during exercise performed under normal conditions (control) and under conditions of restricted blood flow of exercising leg muscles (ischaemia) in nine healthy young men. Blood supply was reduced by 15%-20% by the application of 50 mmHg external pressure over the exercising leg. During 45-min cycling exercise during ischaemia the increase in GH concentration was twice as large as under normal conditions. Despite the below-threshold exercise intensity for activation of the pituitary-adrenocortical system under normal exercise conditions ischaemic exercise elicited cortisol and T3 responses (concentration increases of 83% and 9.5%, respectively). Ischaemic exercise attenuated the decrease of plasma insulin concentration found under normal conditions. The concentrations of testosterone, TSH and fT4 were not changed significantly during exercise performed in either condition. The results support the suggested essential role of muscle metaboreceptors in the control of hormone responses during muscle activity.