Impact of acute exercise intensity on pulsatile growth hormone release in men

To investigate the effects of exercise intensity on growth hormone (GH) rel ease, 10 male subjects were tested on 6 randomly ordered occasions [1 contr ol condition (C), 5 exercise conditions (Ex)]. Serum GH concentrations were measured in samples obtained at 10-min intervals between 0700 and 0900 (ba seline) and 0900 and 1300 (exercise+recovery). Integrated GH concentrations (IGHC) were calculated by trapezoidal reconstruction. During Ex subjects e xercised for 30 min (0900-0930) at one of the following intensities [normal ized to the lactate threshold (LT)]: 25 and 75% of the difference between L T and rest (0.25LT and 0.75LT, respectively), at LT, and at 25 and 75% of t he difference between LT and peak (1.25LT and 1.75LT, respectively). No dif ferences were observed among conditions for baseline IGHC. Exercise+recover y IGHC (mean +/- SE: C = 250 +/- 60; 0.25LT = 203 +/- 69; 0.75LT = 448 +/- 125; LT = 452 +/- 119; 1.25LT = 512 +/- 121; 1.75LT = 713 +/- 115 mu g.l(-1 ).min(-1)) increased linearly with increasing exercise intensity (P < 0.05) . Deconvolution analysis revealed that increasing exercise intensity result ed in a linear increase in the mass of GH secreted per pulse and GH product ion rate [production rate increased from 16.5 +/- 4.5 (C) to 32.1 +/- 5.2 m u g.distribution volume(-1).min(-1) (1.75LT), P < 0.05], with no changes in GH pulse frequency or half-life of elimination. We conclude that the GH se cretary response to exercise is related to exercise intensity in a linear d ose-response pattern in young men.