Growth hormone release following single versus multiple sets of back squats: Total work versus power

Human growth hormone (hGH) is required for normal development, but its role in exercise-induced muscle hypertrophy is not well characterized. The purpose of this study was to determine how total work and mean power affect hGH secretion. Male weight trainers with more than 2 yrs experience in the half squat performed three half-squat exercise trials: One set at 75% 1-RM, one set at 90% 1-RM, and a progressive routine of 75% and 90% sets. The latter dealt with total work by allowing the subjects to lift at their own pace until volitional fatigue, with loads and rest periods controlled. The single-set protocol dealt with power output; the subjects performed as many lifts as possible in 15 sec, using the same workloads as in the progressive routine. Immediate postexercise blood levels of hGH were significantly elevated in the progressive protocol, but not in the singleset protocol, regardless of exercise intensity employed. It was found that the progressive workout involved significantly more work whereas the single bouts were more power oriented. The results demonstrate that total work during exercise is a more important component of hGH release than the amount of power generated.