To assess the influence of exercise training on the growth hormone (GH) response to acute exercise, six untrained males completed a 20-min, high-intensity, constant-load exercise test prior to and after 3 and 6 wk of training (the absolute power output (PO) during each test remained constant,[horizontal bar over]X PO = 182.5 ± 29.5 W). Training increased (pre- vs post-training) oxygen uptake (˙VO2) at lactate threshold (1.57± 0.33 L·min-1 vs 1.97 ± 0.24 L·min-1, P ≤ 0.05), ˙VO2 at 2.5 mM blood lactate concentration ([HLa]) (1.83 ± 0.38 L·min-1 vs 2.33 ± 0.38 L·min-1, P ≤ 0.05), and˙VO2peak (3.15 ± 0.54 L·min-1 vs 3.41 ± 0.47 L·min-1, P ≤ 0.05). Power output at the lactate threshold (PO-LT) increased with training from 103 ± 28 to 132± 23W (P ≤ 0.05). Integrated GH concentration (20 min exercise + 45 min recovery) (μg·L-1 × min) after 3 wk(138 ± 106) and 6 wk (130 ± 145) were significantly lower(P ≤ 0.05) than pre-training (238 ± 145). Plasma epinephrine and norepinephrine responses to training were similar to the GH response (EPI - pre-training = 2447 ± 1110; week 3 = 1046 ± 144; week 6 = 955 ± 322 pmol·L-1; P ≤ 0.05; NE - pre-training = 23.0 ± 5.2; week 3 = 13.4 ± 4.8; week 6 = 12.1± 6.8 nmol·L-1; P ≤ 0.05). These data indicate that the GH and catecholamine response to a constant-load exercise stimulus are reduced within the first 3 wk of exercise training and support the hypothesis that a critical threshold of exercise intensity must be reached to stimulate GH release.
Department of Human Services, Curry School of Education; Department of Internal Medicine, School of Medicine, Exercise Physiology Laboratory, General Clinical Research Center, Health Sciences Center, University of Virginia, Charlottesville, VA 22903; and Division of Pediatric Pharmacology and Critical Care, Rainbow Babies and Children's Hospital, Cleveland, OH 44106
Submitted for publication April 1996.
Accepted for publication December 1996. [/afnote]
We acknowledge the following individuals who provided invaluable assistance to the present project: Sandra Jackson and the nurses in the General Clinical Research Center drew blood and provided patient care; Ginger Bauler and Catherine Kern performed the GH immunoassays; Anita Pettigrew performed the catecholamine assays; Dr. Johannes Veldhuis and Dr. Michael Johnson provided the multiple parameter deconvolution computer program; data management assistance was provided by David Boyd.
Supported in part by NIH General Clinical Research Center Grant RR 00847 and NIH Grant RO1 AG 10997
Address for correspondence: Arthur Weltman, Ph.D., Exercise Physiology Laboratory, Memorial Gymnasium, University of Virginia, Charlottesville, VA 22903.