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

Marcas M. Bamman, James R. Shipp, Jie Jiang, Barbara A. Gower, Gary R. Hunter, Ashley Goodman, Charles L. McLafferty, Randall J. Urban

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Abstract

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.

Original languageEnglish (US)
Pages (from-to)E383-E390
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Volume280
Issue number3 43-3
StatePublished - Mar 1 2001

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Keywords

  • Concentric
  • Creatine kinase
  • Eccentric
  • Insulin-like growth factor I
  • Muscle hypertrophy
  • Resistance exercise

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)

Cite this

Bamman, M. M., Shipp, J. R., Jiang, J., Gower, B. A., Hunter, G. R., Goodman, A., McLafferty, C. L., & Urban, R. J. (2001). Mechanical load increases muscle IGF-I and androgen receptor mRNA concentrations in humans. American Journal of Physiology - Endocrinology and Metabolism, 280(3 43-3), E383-E390.