Effects of an endurance cycling competition on resting serum insulin-like growth factor I (IGF-I) and its binding proteins IGFBP-1 and IGFBP-3. Issue 5 (1st October 2001)

• Record Type: Journal Article
• Authors: Chicharro, J L; López-Calderon, A; Hoyos, J; Martín-Velasco, A I; Villa, G; Villanúa, M A; Lucía, A
• Is Part Of: British journal of sports medicine. Volume 35:Issue 5(2001)
• Page Start: 303
• Page End: 307
• Publication Date: 2001-10-01
• Subjects: cycling -- insulin-like growth factor -- exercise -- endurance -- binding proteins; Sports medicine -- Periodicals; 617.1027
• DOI: 10.1136/bjsm.35.5.303
• Languages: English
• ISSNs: 0306-3674

Abstract

Abstract : Objectives —To determine whether consecutive bouts of intense endurance exercise over a three week period alters serum concentrations of insulin-like growth factor I (IGF-I) and/or its binding proteins. Methods —Seventeen professional cyclists (mean (SEM) Vo 2 max, 74.7 (2.1) ml/kg/min; age, 27 (1) years) competing in a three week tour race were selected as subjects. Blood samples were collected at each of the following time points: t0 (control, before the start of competition), t1 (end of first week), and t3 (end of third week). Serum levels of both total and free IGF-I and IGF binding proteins 1 and 3 (IGFBP-1 and IGFBP-3) were measured in each of the samples. Cortisol levels were measured in nine subjects. Results —A significant (p<0.01) increase was found in total IGF-I and IGFBP-1 at both t1 and t3 compared with to (IGF-I: 110.9 (17.7), 186.8 (12.0), 196.9 (14.7) ng/ml at t0, t1, and t3 respectively; IGFBP-1: 54.6 (6.6), 80.6 (8.0), and 89.2 (7.9) ng/ml at t0, t1, and t3 respectively). A significant (p<0.01) decrease was noted in free IGF-I at t3 compared with both to and t1 (t0 : 0.9 (0.1) ng/ml; t1 : 0.9 (0.1) ng/ml; t3 : 0.7 (0.1) ng/ml); in contrast, IGFBP-3 levels remained stable throughout the race. Conclusions —It would appear that the increase in circulating levels of both IGF-I and its binding protein IGFBP-1 is a short term (one week) endocrine adaptation to endurance exercise. After three weeks of training, total IGF-I and IGFBP-1 remained stable, whereas free IGF-I fell below starting levels.