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

Background: Little is known about the metabolic effects of exercise trainin g in children with cystic fibrosis. The hypothesis for the current study wa s that in patients with declining clinical status, exercise increases circu lating insulin-like growth factors (IGFs) and improves protein kinetics. Methods: This was a prospective intervention study in 10 children with cyst ic Fibrosis who participated in a structured isoenergetic exercise (cycling ) training program for 3 months. Measurements of IGFs, protein kinetics (us ing intravenous [C-13]1-leucine tracer infusions) and nutritional balance s tudies were conducted at baseline and after 3 months. Results: Standard deviation scores of plasma IGF-I, IGF-II, and ICE binding protein (BP)-3 were all decreased at baseline (mean +/- SE: -2.0 +/- 0.2, -2.0 +/- 0.2, -0.6 +/- 0.2. respectively). IGF-I and IGF-II concentrations were significantly higher after exercise training (standard deviation score s -1.4 +/- 0.3 and -1.3 +/- 0.1, respectively; compared with baseline: one- tailed t-test P = 0.03 and 0.002). The standard deviation score of the IGF- I/IGF BP-3 ratio, an indicator of free IGF-I in the circulation, normalized during exercise training (0.0 +/- 0.6 vs. -1.3 +/- 0.2 SD units at baselin e, one-tailed t-test P = 0.04). There was no significant difference in prot ein intake and fasting protein breakdown, oxidation, and protein synthesis or in energy balance and fat absorption. Conclusions: These results show that isoenergetic exercise training can be safely recommended to patients with cystic fibrosis. It provides a positive anabolic stimulus to IGF status but is not sufficient to adequately augmen t protein accretion in patients with diminished nutritional status.