Single muscle fiber adaptations with marathon training

J Appl Physiol (1985). 2006 Sep;101(3):721-7. doi: 10.1152/japplphysiol.01595.2005. Epub 2006 Apr 13.


The purpose of this investigation was to characterize the effects of marathon training on single muscle fiber contractile function in a group of recreational runners. Muscle biopsies were obtained from the gastrocnemius muscle of seven individuals (22 +/- 1 yr, 177 +/- 3 cm, and 68 +/- 2 kg) before, after 13 wk of run training, and after 3 wk of taper. Slow-twitch myosin heavy chain [(MHC) I] and fast-twitch (MHC IIa) muscle fibers were analyzed for size, strength (P(o)), speed (V(o)), and power. The run training program led to the successful completion of a marathon (range 3 h 56 min to 5 h 35 min). Oxygen uptake during submaximal running and citrate synthase activity were improved (P < 0.05) with the training program. Muscle fiber size declined (P < 0.05) by approximately 20% in both fiber types after training. P(o) was maintained in both fiber types with training and increased (P < 0.05) by 18% in the MHC IIa fibers after taper. This resulted in >60% increase (P < 0.05) in force per cross-sectional area in both fiber types. Fiber V(o) increased (P < 0.05) by 28% in MHC I fibers with training and was unchanged in MHC IIa fibers. Peak power increased (P < 0.05) in MHC I and IIa fibers after training with a further increase (P < 0.05) in MHC IIa fiber power after taper. These data show that marathon training decreased slow-twitch and fast-twitch muscle fiber size but that it maintained or improved the functional profile of these fibers. A taper period before the marathon further improved the functional profile of the muscle, which was targeted to the fast-twitch muscle fibers.

Publication types

  • Clinical Trial

MeSH terms

  • Adaptation, Physiological / physiology
  • Adult
  • Exercise / physiology*
  • Exercise Tolerance / physiology*
  • Female
  • Humans
  • Male
  • Muscle Contraction / physiology*
  • Muscle Fibers, Fast-Twitch / cytology
  • Muscle Fibers, Fast-Twitch / physiology*
  • Muscle Fibers, Slow-Twitch / cytology
  • Muscle Fibers, Slow-Twitch / physiology*
  • Muscle, Skeletal / physiology*
  • Running / physiology*