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Reduced exercise-associated response of the GH-IGF-I axis and catecholamines in obese children and adolescents

¹Pediatric Exercise Research Center, Department of Pediatrics, University Children's Hospital, University of California, Irvine, California; ²Child Health & Sports Center, Pediatric Department, Meir General Hospital, Kfar-Saba, Israel; ³Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel; and ⁴Department of Exercise and Sport Science, University of North Carolina, Chapel Hill, North Carolina

Submitted 1 September 2005 ; accepted in final form 23 November 2005

Obesity blunts catecholamine and growth hormone (GH) responses to exercise in adults, but the effect of obesity on these exercise-associated hormonal responses in children is unclear. Therefore, the aim of the present study was to asses the effect of childhood obesity on the counterregulatory hormonal response to acute exercise. Twenty-five obese children (Ob; body mass index > 95%), and 25 age, gender, and maturity-matched normal-weight controls (NW) participated in the study. Exercise consisted of ten 2-min bouts of constant-cycle ergometry above the anaerobic threshold, with 1-min rest intervals between each bout. Pre-, post-, and 120-min postexercise blood samples were collected for circulating components of the GH-IGF-I axis and catecholamines. There were no differences in peak exercise heart rate, serum lactate, and peak O₂ uptake normalized to lean body mass between the groups. Obesity attenuated the GH response to exercise (8.9 ± 1.1 vs. 3.4 ± 0.7 ng/ml in NW and Ob participants, respectively; P < 0.02). No significant differences in the response to exercise were found for other components of the GH-IGF-I axis. Obesity attenuated the catecholamine response to exercise (epinephrine: 52.5 ± 12.7 vs. 18.7 ± 3.7 pg/ml, P < 0.02; norepinephrine: 479.5 ± 109.9 vs. 218.0 ± 26.0 pg/ml, P < 0.04; dopamine: 17.2 ± 2.9 vs. 3.5 ± 1.9 pg/ml, P < 0.006 in NW and Ob, respectively). Insulin levels were significantly higher in the obese children and dropped significantly after exercise in both groups. Despite the elevated insulin levels and the blunted counterregulatory response, none of the participants developed hypoglycemia. Childhood obesity was associated with attenuated GH and catecholamine response to acute exercise. These abnormalities were compensated for, so that exercise was not associated with hypoglycemia, despite increased insulin levels in obese children.

overweight; growth hormone-insulin-like growth factor-I axis; physical activity

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				M. C. Riddell The endocrine response and substrate utilization during exercise in children and adolescents J Appl Physiol, August 1, 2008; 105(2): 725 - 733. [Abstract] [Full Text] [PDF]