Physical capacity influences the response of insulin-like growth factor and its binding proteins to training.
The influence of initial training status on the response of circulating insulin-like growth factor (IGF) and its binding proteins (IGFBP) to prolonged physical training was studied in young men. It was hypothesized that highly standardized training would result in more extensive changes in the circulating IGF system in untrained subjects because of lower fitness level. Seven untrained (UT) and 12 well-trained (WT) individuals performed 11 wk of intense physical training (2-4 h daily). Fasting serum samples were analyzed for total and free IGF-I and -II, for IGFBP-1 to -4, as well as for IGFBP-3 proteolysis. Eleven weeks of physical training resulted in decreased levels of total IGF-I, free IGF-I, and IGFBP-4 in both the UT and WT groups. In the UT group, IGFBP-2 increased, IGFBP-3 decreased [from 4,255 +/- 410 (baseline) to 3,896 +/- 465 (SD) microg/l (week 4); P < 0.05], and IGFBP-3 proteolysis increased [from 28 +/- 8% (baseline) to 37 +/- 7% (week 4) and 39 +/- 12% (week 11); P < 0.05], whereas no significant changes were found in the WT group. In conclusion, intense physical training results in a marked influence on the IGF system and its binding proteins with generally more extensive changes seen in the untrained individuals. Also, prolonged physical training resulted in increased IGFBP-3 proteolysis in previously untrained individuals only, indicating that intense physical training affects trained and untrained individuals differently.
Rosendal
Lars
L
Sports Medicine Research Unit and Copenhagen Muscle Research Centre, Bispebjerg Hospital, DK-2400 Copenhagen, Denmark. LRL@ami.dk
Langberg
Henning
H
Flyvbjerg
Allan
A
Frystyk
Jan
J
Ørskov
Hans
H
Kjaer
Michael
M
D000328:Adult; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism; D018969:Insulin-Like Growth Factor Binding Proteins / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D010447:Peptide Hydrolases / Q000378:metabolism; D010806:Physical Education and Training; D010807:Physical Endurance / Q000502:physiology*; D012016:Reference Values; D013997:Time Factors
D018972:Insulin-Like Growth Factor Binding Protein 3; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I; D010447:Peptide Hydrolases