Growth hormone response to continuous and intermittent exercise.

Abstract

We tested the hypothesis that human growth hormone (hGH) secretion during exercise is related to anaerobic metabolism, and therefore blood lactic acid (LA). Ten males (20 to 30 years) were observed during 40 min of continuous cycle ergometer exercise (CE, 45% of the minimum load which elicited VO2max), and during 20 bouts of intermittent exercise (IE, 1 min on/off at 2x the CE work rate). Continuous and intermittent exercises were used as these are known to result in different LA responses. Resting hGH was 1 to 2 ng/ml. After a lag period, hGH was significantly elevated by 15 min of exercise and thereafter rose continuously in both IE and CE. During IE hGH tended to be higher (12.1 +/- 1.4) than during CE (9.7 +/- 1.6 ng/ml, X +/- SEM), but the difference was not significant. In both exercise conditions free fatty acids demonstrated an initial fall and then a continuous secondary rise with higher peak values during CE (0.52 +/- .06) THAN DURING IE (0.39 +/- .05 mEq/l). Pyruvate (PY) and lactate rose initially during CE, but then declined before reaching steady levels. During IE, LA and PY increased continuously reaching values 3x greater than during CE. Alanine rose progressively during CE and IE, but was significantly higher during IE (442.2 +/- 29.3 vs. 367.9 +/- 30.9 muM). Glucose also tended to be higher during IE (4.67 +/- 0.32) than during CE (4.25 +/- 0.28 mM). Considering CE and IE either together or separately, no physiologically significant correlation was found between hGH and metabolite concentrations, rectal T, or O2 deficit. The results are interpreted to mean that hGH response to work is not directly related to "anaerobiosis".