The growth hormone response to exercise with specific reference to a role in regulating metabolism

Exercise is a potent physiological stimulus for growth hormone (GH) secretion with circulating GH concentrations peaking approximately 30 min after the onset of exercise and remaining elevated for up to 2 h after exercise cessation. Growth hormone concentrations, both at rest and in response to exercise, decline with ageing. The significarice of this decline and the role of the GH response to exercise have not been fully elucidated and this thesis aimed to further understanding in this area. Firstly, this thesis focused on the reproducibility of the GH response to resistance exercise with the aim of determining the appropriateness of this exercise model as a GH stimulus to be used throughout the thesis. GH responses were smaller than previously reported to resistance exercise and a iarge systematic bias in peak GH response was observed for trial order (-4.3 (2.4) Jlg.r1 ), highlighting the need for familiarisation. The second study involved determining whether the decrease in GH response to exercise seen with ageing was of the same magnitude across several different exercise stimuli and which of these stimuli resulted in the largest GH response. In men aged 1825 and 40-50 years old, endurance exercise elicited a greater GH response than sprint or resistance exercise (young: 842 (616) lIS. 531 (346) lIS. 268 (371); Early middle aged: 177 (137), lIS. 8~ (53), lIS. 75 (127) ug.r1.120min-1 responses to endurance, sprint, resistance respectively). The GH response to both sprint and endurance exercise was smaller in the older age group compared to the younger group, with no differences, reported between groups in response to resistance exercise. An analysis of the overall hormone response to the 3 different exercise bouts in the young participants was also .undertaken, revealing a coordinated hormone response to the varying demands of the different exercise modes investigated. The final studies used pegvisomant to block GH action in order to investigate the effects on metabolism before, during, and post-exercise. Surprisingly, considering the lipolytic actions of GH at rest, an increase in fat oxidation was observed during exercise when GH action was limited (CON lIS. PEG (0.39 (0.1) lIS. 0.48 (0.1). Pegvisomant administration also led to different glucose uptake' patterns following exercise.EThOS - Electronic Theses Online ServiceGBUnited Kingdo