Article Text

Download PDFPDF
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
  1. J L Chicharro1,3,
  2. A López-Calderon2,
  3. J Hoyos3,4,
  4. A I Martín-Velasco5,
  5. G Villa6,
  6. M A Villanúa2,
  7. A Lucía3,5
  1. 1Departamento de Enfermería, Facultad de Medicina, Universidad Complutense, Madrid, Spain
  2. 2Departamento de Fisiología
  3. 3Unidad de Investigación en Fisiología del Ejercicio
  4. 4Asociación Deportiva Banesto, Madrid, Spain
  5. 5Departamento de Ciencias Morfológicas y Fisiología, Universidad Europea de Madrid, Madrid, Spain
  6. 6INEF de Castilla y León, Universidad de León, León, Spain
  1. Correspondence to: Professor Chicharro, Departamento de Enfermería, Universidad Complutense, Facultad de Medicina, E-28040 Madrid, Spain jlchicharro{at}


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) Vo2max, 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.

  • cycling
  • insulin-like growth factor
  • exercise
  • endurance
  • binding proteins

Statistics from

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.