Adrenocortical response to one-leg and two-leg exercise on a bicycle ergometer.

Twelve healthy male subjects exercised for 30 min on a bicycle ergometer, using only one leg, at a work load that was nearly exhausting. Nine subjects (group A) showed a marked rise in plasma cortisol concentration (240 +/- 50 nmol x l-1), but in three subjects no such rise occurred (group B). All group B subjects had elevated cortisol levels prior to the period of exercise, which may have inhibited the adrenocortical response. Seven subjects of group A also performed the same work load using both legs. Under this regime, increases in plasma cortisol and aldosterone levels, blood lactate level and heart rate, but not plasma potassium, were significantly smaller than for one-leg exercise. These findings are consistent with the hypothesis that activation of the hypothalamic-pituitary-adrenal (HPA) system during exercise could be mediated through the stimulation of chemoreceptors in the exercising muscles. This effect could be reinforced by HPA stimulation in response to the greater acceleration of heart rate in one-leg exercise. The marked rises in plasma potassium levels might be responsible for the elevation of plasma aldosterone concentration particularly in those experiments when this occurs earlier than, or in the absence of, rises in cortisol concentration.