Nindl, B. C., Alemany, J. A., Rarick, K. R., Staab, J. S., Tuckown, A. P., Welsh, T. T., Gutehunst, D. J., Frykman, P. N., & Harman, E. A. (2006). Differential IGF-I system responses during 8 weeks of resistance vs. generalized physical training in men. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 991.

"Mechanical load is known to consistently induce increased local (i.e. muscle) expression of IGF-I. The extent to which exercise training results in changes in the systemic circulation for the IGF-I system (inclusive of its family of binding proteins (BPs)) has been far less definitive".

This study tested the hypotheses that 1) the family of Insulin Growth Factor-1 binding proteins (IGFBPs) might be more responsive to exercise training than IGF-I itself; and 2) that a training program emphasizing greater localized mechanical load might also result in greater systemic changes in the IGF-I system. Ss were randomly divided into a resistance training group (N = 15) and a generalized physical training group (N = 17) for eight weeks of training (1.5 hr/day, 5 days/wk). The resistance training group engaged in conventional weight lifting exercises, running/hiking, and interval/agility drills, while the physical training group engaged in low-impact callisthenic-type and interval/agility running drills. Blood was sampled at pre, mid- and post training and analyzed by immunoassay for total IGF-I, free IGF-I, IGFBPs 1, 2 and 3, and the acid labile subunit.

No interaction or time effects were observed for total IGF-I, free IGF-I, or IGFBP-1. Time effects were observed for IGFBP-2 and the acid labile subunit. An interaction effect was observed for the resistance training group as IGFBP-3 increased from pre- to mid-, but was no longer significant post-training.

Implication. Some Insulin Growth Factor-1 binding proteins are more responsive to exercise stress than IGF-I itself. Changes are not specific to exercise modality suggesting that changes in the systemic IGF-I system during exercise training may be a generalized metabolic response and not a response specific to exercise modality or muscle overload.

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