Increase in serum growth hormone induced by electrical stimulation of muscle combined with blood flow restriction.

The purpose of this study was to investigate the role of muscle metaboreflex on exercise-induced growth hormone (GH) secretion. In order to accumulate metabolites within exercised muscle with minimized central motor activity, electromyostimulation (EMS) was performed combined with blood flow restriction (BFR). Seven men performed one-legged isometric knee extension evoked by EMS (frequency, 20 Hz; pulse duration, 400 μs; on-off ratio, 3-1 s). Just before the exercise, proximal portion of either a stimulated thigh (ST) or a non-stimulated thigh (NT) was compressed at 150 mmHg with an air-pressure cuff for the purpose of BFR. The compression was kept throughout the exercise session, and was released 2 min after the end of the exercise. Two exercise sessions (ST(BFR), BFR for ST; NT(BFR), BFR for NT) were separated by 1 week. ST(BFR) was aimed to accumulate metabolites within exercised muscle, whereas NT(BFR) was aimed to match mechanical stress with ST(BFR) without accumulating metabolites. Blood samples for hormonal measurements were taken from the antecubital vein before and after the exercise. Blood lactate increased immediately after the exercise in the NT(BFR), whereas it increased after the cuff deflation in the ST(BFR), suggesting that locally produced metabolites were retained and accumulated within the exercised muscle in the ST(BFR). Although serum cortisol and plasma noradrenaline increased in a similar manner in two conditions, serum immunoreactive GH (irGH) increased only in the ST(BFR). These results suggest that muscle metaboreflex plays an important role in the exercise-induced GH secretion, at least in terms of irGH secretion.