Mechanical load increases muscle IGF-I and androgen receptor mRNA concentrations in humans.

Academic Article


  • 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.
  • Published In


  • Adult, Biomechanical Phenomena, Creatine Kinase, Exercise, Female, Humans, Hypertrophy, Insulin-Like Growth Factor Binding Protein 4, Insulin-Like Growth Factor I, Kinetics, Male, Muscle, Skeletal, RNA, Messenger, Receptors, Androgen, Reverse Transcriptase Polymerase Chain Reaction, Testosterone, Weight-Bearing
  • Digital Object Identifier (doi)

    Author List

  • Bamman MM; Shipp JR; Jiang J; Gower BA; Hunter GR; Goodman A; McLafferty CL; Urban RJ
  • Start Page

  • E383
  • End Page

  • E390
  • Volume

  • 280
  • Issue

  • 3