Overnight responses of the circulating IGF-I system after acute, heavy-resistance exercise

This study evaluated the individual components of the insulin-like growth factor I (IGF-I) system [i.e., total and free IGF-I, insulin-like growth factor binding protein (IGFBP)-2 and -3, and the acid-labile subunit (ALS)] in 10 young, healthy men (age: 22 +/- 1 yr, height: 177 +/- 2 cm, weight: 79 +/- 3 kg, body fat: 11 +/- 1%) overnight for 13 h after two conditions: a resting control (Con) and an acute, heavy-resistance exercise protocol (Ex). The Ex was a high-volume, multiset exercise protocol that alternated between 10- and 5-repetition maximum sets with 90-s rest periods between sets. The Ex was performed from 1500 to 1700; blood was obtained immediately postexercise and sampled throughout the night (every 10 min for the first hour and every hour thereafter) until 0600 the next morning. For the first hour, significant differences (P < or = 0.05) were only observed for IGFBP-3 (Ex: 3,801 > Con: 3,531 ng/ml). For the overnight responses, no differences were observed for total or free IGF-I or IGFBP-3, whereas IGFBP-2 increased (Ex: 561 > Con: 500 ng/ml) and ALS decreased (Ex: 35 < Con: 39 microg/ml) after exercise. The results from this study suggest that the impact that resistance exercise exerts on the circulating IGF-I system is not in the alteration of the amount of IGF-I but rather of the manner in which IGF-I is partitioned among its family of binding proteins. Thus acute, heavy-resistance exercise can lead to alterations in the IGF-I system that can be detected in the systemic circulation.