Obesity Attenuates the Growth Hormone Response to Exercise1

Resting serum GH concentrations are decreased in obesity. In nonobese (NonOb) individuals, acute exercise of sufficient intensity increases GH levels; however, conflicting data exist concerning the GH response to exercise in obese individuals. To examine the exercise-induced GH response in obese individuals, we studied 8 NonOb, 11 lower body obese (LBO), and 12 upper body obese (UBO) women before, during, and after 30 min (0800–0830 h) of treadmill exercise at 70% oxygen consumption peak. Blood samples were taken every 5 min (0700–1300 h) and were analyzed for GH concentrations with a sensitive (0.002 μg/L) chemiluminescence assay. The impact of 16 weeks of aerobic exercise training on the GH response to exercise was also examined in the obese women. In response to exercise, the 6-h integrated GH concentration was significantly greater (P < 0.05) in the NonOb women (1006 ± 220 min/μg·L) than in either of the obese groups (LBO, 435 ± 136; UBO, 189 ± 26 min/μg·L). No differences were found between the LBO and UBO women. The increased integrated GH concentrations could be accounted for by a greater 6-h GH production rate [micrograms per L distribution volume (Lv)] in the NonOb women than in either of the obese groups (NonOb, 45.6 ± 12.3; LBO, 16.9 ± 1.2; UBO, 8.7± 0.64 μg/LV; P < 0.05). This increase was attributed to a greater mass of GH secreted per pulse in the NonOb women (NonOb, 10.8 ± 2.5; LBO, 4.9 ± 0.8; UBO, 4.0 ± 0.5 μg/LV; P < 0.05, NonOb vs. both obese groups). After 16 weeks of aerobic training, maximal oxygen consumption increased from 44.7 ± 2.2 to 48.5 ± 1.9 mL/kg fat-free mass·min; P < 0.05), but no significant change in body composition occurred in the 10 obese women who completed the training. No change was observed in the GH response to exercise after training (n = 10; pre, 379 ± 144; post, 350 ± 55 min/μg·L). In conclusion, the GH response to exercise was attenuated in the obese women compared to NonOb women. Short term aerobic training improved fitness, but did not increase the GH response to exercise.