Introduction: The pulsatile secretion pattern of growth hormone (GH) is an important parameter of GH action at peripheral tissues, and more information is needed on how exercise impacts GH secretion. This study hypothesized that both aerobic and resistance exercise would exhibit dose-response relationships with respect to exercise duration and 20-h postexercise GH secretion.
Methods: Eight healthy men randomly completed five separate conditions: 1) control (no exercise; CON), 2) a moderate-duration (1-h) aerobic exercise session (MA), 3) a long-duration (2-h) aerobic exercise session (LA), 4) a moderate-duration (1-h) resistance exercise session (MR), and 5) a long-duration (2-h) resistance exercise session (LR). Exercise intensity, diet, sleep, and physical activity were strictly controlled during each condition, and blood was sampled postexercise every 20 min for 20 h, and GH secretion parameters were analyzed via cluster and deconvolution analyses.
Results: Only the 2-h aerobic exercise bout resulted in a significant amplification of GH secretion as evidenced by increases in GH burst peak amplitude (∼100%), basal GH secretion rate (∼127%), total GH basal secretion (∼120%), total pulsatile secretion (∼88%), and total GH secretion (∼89%) over the control (i.e., no exercise) condition. GH secretions for the resistance exercise conditions were not different from control.
Conclusions: The fact that the 2-h aerobic exercise condition resulted in higher energy expenditure than the other exercise conditions could offer a partial explanation for the greater GH amplification because of the metabolic effects that GH exerts in stimulating postexercise lipolysis. We conclude that extending the duration of aerobic exercise, but not resistance exercise, from 1- to 2-h significantly amplifies GH secretion during a 20-h period.