Insulin-like growth factors and leucine kinetics during exercise training in children with cystic fibrosis

Exercício aeróbico, treinamento de força muscular e testes de aptidão física para adolescentes com fibrose cística: revisão da literatura

São reconhecidos os benefícios da prática do exercício físico regular para pacientes com fibrose cística. Entretanto, poucos estudos envolvem pacientes adolescentes. O objetivo deste artigo foi revisar os efeitos da prática regular de exercícios aeróbicos e de força e resistência muscular para adolescentes com fibrose cística. Os principais testes de aptidão física para esta faixa etária e a importância deles para melhora do prognóstico e tratamento da doença também foram avaliados. As informações foram coletadas a partir de livro-texto e artigos publicados na literatura nacional e estrangeira nas seguintes bases de dados: LILACS, MEDLINE/PubMed, Biblioteca Cochrane e SciELO, abrangendo o período de 1994 a 2004. Foram utilizados os termos "exercise" e "cystic fibrosis" para seleção dos artigos. Esta pesquisa demonstrou que a prática de exercício aeróbico e treinamento de força muscular melhoram a desobstrução da árvore brônquica, diminuem a queda progressiva da função pulmonar, aumentam a massa muscular e a resistência ao exercício, promovem o desenvolvimento ósseo e melhoram a auto-estima e a qualidade de vida. Os melhores resultados foram obtidos com os programas de treinamento assistido, devido a sua maior regularidade.

Physical capacity influences the response of insulin-like growth factor and its binding proteins to training

The influence of initial training status on the response of circulating insulin-like growth factor (IGF) and its binding proteins (IGFBP) to prolonged physical training was studied in young men. It was hypothesized that highly standardized training would result in more extensive changes in the circulating IGF system in untrained subjects because of lower fitness level. Seven untrained (UT) and 12 well-trained (WT) individuals performed 11 wk of intense physical training (2-4 h daily). Fasting serum samples were analyzed for total and free IGF-I and -II, for IGFBP-1 to -4, as well as for IGFBP-3 proteolysis. Eleven weeks of physical training resulted in decreased levels of total IGF-I, free IGF-I, and IGFBP-4 in both the UT and WT groups. In the UT group, IGFBP-2 increased, IGFBP-3 decreased [from 4,255 +/- 410 (baseline) to 3,896 +/- 465 (SD) microg/l (week 4); P < 0.05], and IGFBP-3 proteolysis increased [from 28 +/- 8% (baseline) to 37 +/- 7% (week 4) and 39 +/- 12% (week 11); P < 0.05], whereas no significant changes were found in the WT group. In conclusion, intense physical training results in a marked influence on the IGF system and its binding proteins with generally more extensive changes seen in the untrained individuals. Also, prolonged physical training resulted in increased IGFBP-3 proteolysis in previously untrained individuals only, indicating that intense physical training affects trained and untrained individuals differently.

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

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.