Differences In the GH-IGF-I Axis In Children of Different Weight and Fitness Status

Objective: To determine if differences in the GH-IGF-I axis exist between children of high and low aerobic fitness who are obese or of normal weight. Design: 124 children (ages 8-11) divided into four groups based on BMI and VO 2max (mL O 2/kg fat free mass(FFM)/min): normal weight - high-fit (NH), normal weight - low-fit (NL), obese - high-fit (OH), and obese - low-fit (OL). Height, weight, skinfolds, body mass index (BMI), body fat percentage and predicted VO 2max (both ml/kg/min and ml/kg FFM/min) were assessed. Resting growth hormone (GH), total insulin-like growth factor 1 (total IGF-I), free insulin-like growth factor 1(free IGF-I), and insulin were measured using morning fasting blood samples. Results: GH was greater in the NH group compared to the OL group only (p\u3c0.01). No group differences existed for either total IGF-I (p=0.53) or free IGF-I (p=0.189). Insulin was greater in the OH and OL groups than the NH and NL groups (p\u3c0.01). With groups combined (or overall), insulin and free IGF-I were related to fitness (insulin - ml/kg/min: r=-0.226, p\u3c0.05 and ml/kg FFM/min: r=-0.212, p\u3c0.05; free IGF-I - ml/kg/min: r=-0.219, p\u3c0.01 and ml/kg FFM/min: r=-0.272, p\u3c0.05). Conclusions: Fitness may contribute to the obesity related reduction of GH that may be involved with weight gain