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.

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"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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