Effect of acid-base balance on the growth hormone response to acute high-intensity cycle exercise.

To investigate the effect of acid-base balance on serum human growth hormone (hGH) concentration after an acute high-intensity anaerobic exercise bout, 10 untrained but normally active men [age, 24.6 +/- 1.5 (SE) yr] participated in a randomized double-blind counterbalanced experiment. Each subject reported in a fasted state at the same time of day for two experimental sessions separated by 1 wk. For each session, subjects were administered a decaffeinated tea solution containing either 0.3 g NaHCO3/kg body wt [alkalosis (ALK)] or 0.04 g NaCl/kg body wt [control (CTRL)] over a 45-min ingestion period. Venous blood samples were obtained before [baseline (BL)] and 75 min after the ingestion period, as well as postexercise at 0, 5, 10, 15, 20, and 30 min. The exercise task immediately followed the preexercise blood draw and consisted of 90 s of maximal-effort cycle ergometry against an opposing force of 0.49 N (0.05 kg)/kg body wt. There were no differences between the ALK and CTRL conditions in mean or peak power output or total work during the exercise task. Whole blood pH was significantly (P < or = 0.05) elevated in ALK above CTRL at all time points except BL. Postexercise serum hGH concentration significantly increased above BL at 10, 15, 20, and 30 min in CTRL and at 20 and 30 min in ALK. The hGH concentration was significantly lower in ALK than in CTRL at 15, 20, and 30 min postexercise. These data indicate that an increase in blood hydrogen ion concentration may be partly responsible for the hGH response to acute high-intensity anaerobic exercise.