Effects of resistance training on insulin-like growth factor-I and IGF binding proteins.
OBJECTIVE
Our goal was to determine the effects resistance training on circulating IGF-I and on two of its major binding proteins, IGFBP-1 and IGFBP-3. Additional goals were to compare the time course of hormonal changes with the time course of strength changes and to determine the effect of training volume on the extent of hormonal changes.


METHODS
Thirty-one men and women (mean age = 37 +/- 7 yr) completed a 25-wk, 3 d x wk(-1) program in which they performed single-set resistance training (1-SET, N = 11), multiple-set resistance training (3-SET, N = 11), or no exercise (Control, N = 9). Before training, and after 13 and 25 wk of training, blood hormones were analyzed and strength was assessed as the sum of one-repetition maximum (1-RM) for leg extension and chest press exercises.


RESULTS
During the first 13 wk of resistance training, circulating IGF-I increased by approximately 20% in both the 1-SET and 3-SET groups (P = 0.041). No further increases occurred between 13 and 25 wk. In the 3-SET group, IGFBP-3 decreased 20% between 13 and 25 wk (P = 0.008). Training did not alter IGFBP-1. Increases in 1-RM strength occurred mainly during the first 13 wk of training and were significantly higher with 3-SET training compared to 1-SET.


CONCLUSIONS
These findings indicate that increased circulating IGF-I may, at least in part, mediate increases in strength that result from resistance training.
Borst
S E
SE
University of Florida Department of Pharmacology, Gainesville, FL 32610, USA. sborst@pharmacology.ufl.edu
De Hoyos
D V
DV
Garzarella
L
L
Vincent
K
K
Pollock
B H
BH
Lowenthal
D T
DT
Pollock
M L
ML
D000328:Adult; D000704:Analysis of Variance; D005260:Female; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010809:Physical Fitness / Q000502:physiology*; D014891:Weight Lifting / Q000502:physiology*
D018972:Insulin-Like Growth Factor Binding Protein 3; D007334:Insulin-Like Growth Factor I