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Pediatr Res. 2002 Oct;52(4):491-7.

The effect of endurance-type exercise training on growth mediators and inflammatory cytokines in pre-pubertal and early pubertal males.

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Center for the Study of Health Effects of Exercise in Children, University of California, Irvine, College of Medicine, Orange, California, USA.


Recent studies demonstrate an unexpected reduction in circulating levels of IGF-I after 5 wk of endurance-type exercise training in adolescent boys and girls and prepubertal girls. We hypothesized that the reduction in IGF-I would be accompanied by a training-associated stimulation of proinflammatory cytokines IL-1beta, IL-6, or tumor necrosis factor-alpha (TNF-alpha), each of which can inhibit the GH-->IGF-I axis. Healthy boys (age range 9-11 y old, mean Tanner 1.7) volunteered for the study and were randomized to control (n = 14) and training groups (n = 12) for 5 wk. After the intervention, significant increase in fitness was observed in the training group but not control group. Although IGF-I was correlated at baseline to peak oxygen consumption in all subjects, there was a significant decrease in IGF-I and IGF binding protein-3 in the training subjects (-12.8 +/- 7.3% and -17.5 +/- 7%, respectively, p < 0.05). In contrast, IGF binding protein-2, known to inhibit anabolic effects of IGF-I, increased in the training subjects (27.8 +/- 11%, p < 0.02) as did IL-1beta and TNF-alpha (51.5 +/- 30.22%, p < 0.02, and 44.5 +/- 23.2%, p < 0.02, respectively). Finally, we also found that GHBP was inversely correlated with fitness, suggesting altered GH function in more-sedentary boys. Thus, these data support the hypothesis that a sustained increase in physical activity can stimulate proinflammatory cytokines, which may contribute to suppression of the GH-->IGF-I axis. Physical activity can influence growth and development through its influence on anabolic and catabolic mediators.

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