Threshold increases in plasma growth hormone in relation to plasma catecholamine and blood lactate concentrations during progressive exercise in endurance-trained athletes

Plasma human growth hormone (HGH]), adrenaline (A]), noradrenaline (NA]) and blood lactate (La^–]_b) concentrations were measured during progressive, multistage exercise on a cycle ergometer in 12 endurance-trained athletes aged 32.0 (SEM 2.0) years]. Exercise intensities (3 min each) were increased by 50 W until the subjects felt exhausted. Venous blood samples were taken after each intensity. The HGH] and catecholamine concentrations increased negligibly during exercise of low to moderate intensities revealing an abrupt rise at the load corresponding to the lactate threshold (La^–]-T). Close correlations (P < 0.001) were found between La^–]_b and plasma HGH] (r = 0.64), A] (r = 0.71) and NA] (r = 0.81). The mean threshold exercise intensities for HGH], A] and NA], detected by log-log transformation, 154 (SEM 19) W, 162 (SEM 15) W and 160 (SEM 17) W, respectively] were not significantly different from the La^–]-T 161 (SEM 12) W]. The results indicated that the threshold rise in plasma HGH] followed the patterns of plasma catecholamine and blood lactate accumulation during progressive exercise in the endurancetrained athletes.