Mechanical load increases muscle IGF-I and androgen receptor mRNA concentrations in humans.
The mechanism(s) of load-induced muscle hypertrophy is as yet unclear, but increasing evidence suggests a role for locally expressed insulin-like growth factor I (IGF-I). We investigated the effects of concentric (CON) vs. eccentric (ECC) loading on muscle IGF-I mRNA concentration. We hypothesized a greater IGF-I response after ECC compared with CON. Ten healthy subjects (24.4 +/- 0.7 yr, 174.5 +/- 2.6 cm, 70.9 +/- 4.3 kg) completed eight sets of eight CON or ECC squats separated by 6-10 days. IGF-I, IGF binding protein-4 (IGFBP-4), and androgen receptor (AR) mRNA concentrations were determined in vastus lateralis muscle by RT-PCR before and 48 h after ECC and CON. Serum total testosterone (TT) and IGF-I were measured serially across 48 h, and serum creatine kinase activity (CK), isometric maximum voluntary contraction (MVC), and soreness were determined at 48 h. IGF-I mRNA concentration increased 62% and IGFBP-4 mRNA concentration decreased 57% after ECC (P < 0.05). Changes after CON were similar but not significant (P = 0.06-0.12). AR mRNA concentration increased (P < 0.05) after ECC (63%) and CON (102%). Serum TT and IGF-I showed little change. MVC fell 10% and CK rose 183% after ECC (P < 0.05). Perceived soreness was higher (P < 0.01) after ECC compared with CON. Results indicate that a single bout of mechanical loading in humans alters activity of the muscle IGF-I system, and the enhanced response to ECC suggests that IGF-I may somehow modulate tissue regeneration after mechanical damage.
Bamman
M M
MM
Department of Human Studies, University of Alabama at Birmingham, Birmingham, AL 35294, USA. mbamman@uab.edu
Shipp
J R
JR
Jiang
J
J
Gower
B A
BA
Hunter
G R
GR
Goodman
A
A
McLafferty
C L
CL
Urban
R J
RJ
D000328:Adult; D001696:Biomechanical Phenomena; D003402:Creatine Kinase / Q000097:blood; D015444:Exercise; D005260:Female; D006801:Humans; D006984:Hypertrophy; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000235:genetics; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000235:genetics*; D007700:Kinetics; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D012333:RNA, Messenger / Q000378:metabolism*; D011944:Receptors, Androgen / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013739:Testosterone / Q000097:blood; D016474:Weight-Bearing
D018974:Insulin-Like Growth Factor Binding Protein 4; D012333:RNA, Messenger; D011944:Receptors, Androgen; D013739:Testosterone; D007334:Insulin-Like Growth Factor I; D003402:Creatine Kinase