Dynamics of GH secretion during incremental exercise in obesity, before and after a short period of training at different work-loads

Background Growth hormone (GH) secretion is normally sensitive to physical exercise. Intensity and duration of exercise, fitness and age can all influence the GH response to exercise. In obesity, GH secretion is decreased both in basal conditions and in response to exercise. Objective To analyse the dynamics of GH response to a progressive cycloergometric test, conducted up to exhaustion, in adult normal subjects and obese patients, after a reconditioning program at different workloads. Design and methods We studied eight lean subjects (four men, mean age 34·3 years, range 26-47 years, mean body mass index (BMI) 22·1 kg/m²). GH was sampled at baseline and during the last 30 s of each power output increase. Anaerobic threshold (AT) was detected by the V-slope method. The same test was carried out in 16 obese subjects (seven men, mean age 39·1 years, range 20-59 years, mean BMI 35·8 kg/m ²) and repeated after a 4-week reconditioning program consisting of aerobic workout (Group A, eight subjects, three men, mean age 40·5 years, range 22-59 years, mean BMI 33·6 kg/m²), and aerobic plus anaerobic work (group B, eight subjects, four men, mean age 37·6 years, range 20-56 years, mean BMI 38·0 kg/m²) for 6 days/week, with no dietary restrictions. Results Mean exercise peak occurred at higher intensity in controls (140 vs 110 W, P < 0·05), and AT exceeded at higher work outputs than in obese subjects (102 vs 74 W, P < 0·05). In controls, GH response to exercise was prompt and further sustained after AT; in obese subjects, GH increased slowly and insignificantly before AT, thereafter it increased to lower levels than in controls (P < 0·001). Following the reconditioning period, both Group A and Group B of obese subjects failed to improve exercise performance as well as GH response to exercise before AT; beyond AT, a greater GH response to exercise occurred in Group B than Group A (7·59 ± 0·32 μg/l at peak of exercise) with significantly different Delta AUCs (Area Under the Curves) following AT: 30·5 ± 12 μg.min/l in Group A vs 124·2 ± 38 μg.min/l in Group B, P < 0·05. Conclusions Our results confirm the blunted GH response to exercise in obese adults when compared to lean counterparts. With obesity, aerobic training poorly increases the GH response beyond AT, while supplemental anaerobic workload appears to increase GH response beyond AT. These observations may have implications for the prescription of physical exercise, which is one of the recommendations in the management of obesity.