title: Human growth hormone response to repeated bouts of aerobic exercise.
abstract: We examined whether repeated bouts of exercise could override growth hormone (GH) auto-negative feedback. Seven moderately trained men were studied on three occasions: a control day (C), a sequential exercise day (SEB; at 1000, 1130, and 1300), and a delayed exercise day (DEB; at 1000, 1400, and 1800). The duration of each exercise bout was 30 min at 70% maximal O2 consumption (VO2max) on a cycle ergometer. Standard meals were provided at 0600 and 2200. GH was measured every 5-10 min for 24 h (0800-0800). Daytime (0800-2200) integrated GH concentrations were approximately 150-160% greater during SEB and DEB than during C: 1,282 +/- 345, 3,192 +/- 669, and 3,389 +/- 991 min.microgram.l-1 for C, SEB, and DEB, respectively [SEB > C (P < 0.06), DEB > C (P < 0.03)]. There were no differences in GH release during sleep (2300-0700). Deconvolution analysis revealed that the increase in 14-h integrated GH concentration on DEB was accounted for by an increase in the mass of GH secreted per pulse (per liter of distribution volume, lv): 7.0 +/- 2.9 and 15.9 +/- 2.6 micrograms/lv for C and DEB, respectively (P < 0.01). Comparison of 1.5-h integrated GH concentrations on the SEB and DEB days (30 min exercise + 60 min recovery) revealed that, with each subsequent exercise bout, GH release apparently increased progressively, with a slightly greater increase on the DEB day [SEB vs. DEB: 497 +/- 162 vs. 407 +/- 166 (bout 1), 566 +/- 152 vs. 854 +/- 184 (bout 2), and 633 +/- 149 vs. 1,030 +/- 352 min.microgram.l-1 (bout 3), P < 0.05]. We conclude that the GH response to acute aerobic exercise is augmented with repeated bouts of exercise.
authors.affiliation: Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Kanaley
authors.forename: J Y
authors.initials: JY
authors.lastname: Weltman
authors.forename: J D
authors.initials: JD
authors.lastname: Veldhuis
authors.forename: A D
authors.initials: AD
authors.lastname: Rogol
authors.forename: M L
authors.initials: ML
authors.lastname: Hartman
authors.forename: A
authors.initials: A
authors.lastname: Weltman
mesh_terms: D000328:Adult; D001823:Body Composition / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D013006:Growth Hormone / Q000097:blood*; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D013997:Time Factors
chemical_list: D013006:Growth Hormone