Measuring mechanical properties, including isotonic fatigue, of fast and slow MLC/mIgf-1 transgenic skeletal muscle

Ann Biomed Eng. 2008 Jul;36(7):1281-90. doi: 10.1007/s10439-008-9496-x. Epub 2008 Apr 15.


Contractile properties of fast-twitch (EDL) and slow-twitch (soleus) skeletal muscles were measured in MLC/mIgf-1 transgenic and wild-type mice. MLC/mIgf-1 mice express the local factor mIgf-1 under the transcriptional control of MLC promoter, selectively activated in fast-twitch muscle fibers. Isolated muscles were studied in vitro in both isometric and isotonic conditions. We used a rapid "ad hoc" testing protocol that measured, in a single procedure, contraction time, tetanic force, Hill's (F-v) curve, power curve and isotonic muscle fatigue. Transgenic soleus muscles did not differ from wild-type with regard to any measured variable. In contrast, transgenic EDL muscles displayed a hypertrophic phenotype, with a mass increase of 29.2% compared to wild-type. Absolute tetanic force increased by 21.5% and absolute maximum power by 34.1%. However, when normalized to muscle cross-sectional area and mass, specific force and normalized power were the same in transgenic and wild-type EDL muscles, revealing that mIgf-1 expression induces a functional hypertrophy without altering fibrotic tissue accumulation. Isotonic fatigue behavior did not differ between transgenic and wild-type muscles, suggesting that the ability of mIgf-1 transgenic muscle to generate a considerable higher absolute power did not affect its resistance to fatigue.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Animals, Genetically Modified
  • Biomechanical Phenomena / instrumentation
  • Biomechanical Phenomena / methods*
  • Female
  • Insulin-Like Growth Factor I / physiology*
  • Male
  • Mice
  • Muscle Contraction / physiology*
  • Muscle Fatigue / physiology*
  • Muscle Fibers, Fast-Twitch / physiology*
  • Muscle Fibers, Slow-Twitch / physiology*
  • Muscle, Skeletal / physiology*
  • Myosin Light Chains / physiology*


  • Myosin Light Chains
  • Insulin-Like Growth Factor I