Plasma growth hormone is elevated immediately after resistance exercise with electrical stimulation and voluntary muscle contraction.

Resistance exercise is a physiological stimulus for acute increases in growth hormone (GH) secretion, and it also causes lactate accumulation and stimulates norepinephrine (NE) secretion as a sympathetic nervous response. The hybrid exercise method (HYB) is a novel resistance exercise method that combines a voluntary concentric muscle contraction and an electrically stimulated eccentric muscle contraction. This study was designed to compare the hormonal responses of HYB with typical weight training (WT), as regards GH, lactate, and NE. Twenty-four healthy male subjects (20-27 years) were divided into the HYB group and the WT group. All the subjects performed bilateral leg exercises with 10 sets of 10 reciprocal 2-second (45 degrees /sec) knee flexion-and-extension contractions, and with 1-min interset rest intervals. Plasma concentrations of GH, lactate, and NE were determined before exercise and immediately after exercise (0 min) as well as at 15, 30, 60, and 120 min. The plasma concentrations of GH and lactate were significantly increased immediately after HYB or WT (P < 0.05). Moreover, the degree of the increases of GH and lactate after HYB was significantly higher than that after WT (P < 0.05). The plasma concentration of NE was significantly increased after HYB or WT (P < 0.01), but no significant difference was observed between the two groups. These results indicate that HYB is more efficient in stimulating acute increases in plasma GH and lactate without enhancing sympathetic nerve stimulation, compared to WT. Therefore, HYB may be an effective countermeasure to muscle disuse associated with bed rest or spaceflight.