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Single-fiber MHC polymorphic expression is unaffected by sprint cycle training.

Allen C Parcell1, Robert D Sawyer, Micah J Drummond

  • 1Department of Exercise Sciences, Human Performance Research Center, Brigham Young University, Provo, UT 84602, USA. allen_parcell@byu.edu

Medicine and Science in Sports and Exercise
|July 15, 2005
PubMed
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High-intensity sprint cycle training improves performance by altering myosin heavy chain (MHC) isoforms. This training increases MHC IIa and decreases MHC IIx in the vastus lateralis, without changing hybrid fiber content.

Area of Science:

  • Exercise Physiology
  • Muscle Biology

Background:

  • Sprinting performance relies on specific muscle fiber types and their myosin heavy chain (MHC) composition.
  • Understanding how training modalities influence MHC expression is crucial for optimizing athletic development.

Purpose of the Study:

  • To investigate changes in single-fiber MHC composition following high-intensity, short-duration sprint cycle training.
  • To determine the effects of this training on vastus lateralis muscle and sprinting performance.

Main Methods:

  • Ten untrained males underwent 8 weeks of progressive sprint cycle training.
  • Training intensity and volume increased over the 8 weeks.
  • Muscle biopsies and a 30-s sprint test were conducted pre- and post-training.

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Main Results:

  • Sprint performance, including mean power and total work, significantly improved.
  • A significant reduction in MHC IIx isoform content was observed (2.0% to 0.2%).
  • MHC IIa content showed a trend towards increase, and hybrid fiber content remained unchanged.

Conclusions:

  • Eight weeks of high-intensity sprint cycle training is sufficient to enhance sprinting performance.
  • The observed performance improvements correlate with an increase in MHC IIa and a decrease in MHC IIx in the vastus lateralis.
  • This training protocol does not alter the proportion of hybrid muscle fibers.