Human growth hormone response to repeated bouts of aerobic exercise. J. Appl. Physiol. 83(5): 1756-1761, 1997.-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 O 2 consumption (V O 2

more »

... ax ) 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 ϳ150-160% greater during SEB and DEB than during C: 1,282 Ϯ 345, 3,192 Ϯ 669, and 3,389 Ϯ 991 min·µg·l Ϫ1 for C, SEB, and DEB, respectively [SEB Ͼ C (P Ͻ 0.06), DEB Ͼ C (P Ͻ 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, l v ): 7.0 Ϯ 2.9 and 15.9 Ϯ 2.6 µg/l v for C and DEB, respectively (P Ͻ 0.01). Comparison of 1.5-h integrated GH concentrations on the SEB and DEB days (30 min exercise ϩ 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 Ϯ 162 vs. 407 Ϯ 166 (bout 1), 566 Ϯ 152 vs. 854 Ϯ 184 (bout 2), and 633 Ϯ 149 vs. 1,030 Ϯ 352 min·µg·l Ϫ1 (bout 3), P Ͻ 0.05]. We conclude that the GH response to acute aerobic exercise is augmented with repeated bouts of exercise.