LOW INTENSITY RESISTANCE EXERCISE FOLLOWING HIGH INTENSITY RESISTANCE EXERCISE STIMULATES GROWTH HORMONE SECRETION IN MEN

Abstract

To examine endogenous growth hormone response to various heavy resistance exercise protocols, eight active male subjects performed five resistance exercise protocols randomly on separate days. The protocols were categorized into three types of exercise with different objectives. The first type was resistance exercise which consisted of five sets at 90% of one repetition maximum (IRM) with 3-min rest periods between sets (Strength type: S). The second type was resistance exercise which consisted of nine sets at 40–80% of 1RM with 30 sec or 3-min rest periods between sets (Hypertrophy type: H). The third type included 3 separated protocols, each of which consisted of a combination of S and H (Combination type). The combination type was characterized by an additional relatively low intensity set following a series of high intensity sets (five sets at 90% of 1RM). The load used in the additional set was either 90% of 1RM (C90), 70% of 1RM (C70) or 50% of 1RM (C50). The exercise performed in all sets of all protocols was bilateral knee extension repeated until exhaustion. Serum growth hormone concentration (GH) and whole blood lactate concentration were determined preexercise and at 0–60 min postexercise. Relative changes in thigh girth (%GIRTH) and knee extension maximal isometric force were determined preexercise and immediately postexercise. Minor but significant changes in peak growth hormone concentration (GHpeak) were observed in S and C90. GHpeak in H was the highest value of all protocols. On the other hand, GHpeak in C50 showed a significantly (P < 0.05) higher increase than in S and a relatively higher increase than in C70. In addition, peak lactate concentration and %GIRTH correlated significantly (P < 0.05) with GHpeak. These findings suggest that an additional low intensity set (50% of 1RM) following a series of high intensity sets significantly increases GH secretion. It is possible that factors related to greater metabolite changes in working muscle resulted in the greater GH response.