Functional properties of human muscle fibers after short-term resistance exercise training

Am J Physiol Regul Integr Comp Physiol. 2002 Aug;283(2):R408-16. doi: 10.1152/ajpregu.00120.2002.


The aim of this study was to assess the relationships between human muscle fiber hypertrophy, protein isoform content, and maximal Ca(2+)-activated contractile function following a short-term period of resistance exercise training. Six male subjects (age 27 +/- 2 yr) participated in a 12-wk progressive resistance exercise training program that increased voluntary lower limb extension strength by >60%. Single chemically skinned fibers were prepared from pre- and posttraining vastus lateralis muscle biopsies. Training increased the cross-sectional area (CSA) and peak Ca(2+)-activated force (P(o)) of fibers containing type I, IIa, or IIa/IIx myosin heavy chain by 30-40% without affecting fiber-specific force (P(o)/CSA) or unloaded shortening velocity (V(o)). Absolute fiber peak power rose as a result of the increase in P(o), whereas power normalized to fiber volume was unchanged. At the level of the cross bridge, the effects of short-term resistance training were quantitative (fiber hypertrophy and proportional increases in fiber P(o) and absolute power) rather than qualitative (no change in P(o)/CSA, V(o), or power/fiber volume).

Publication types

  • Clinical Trial
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adaptation, Physiological
  • Adult
  • Biomechanical Phenomena
  • Biopsy
  • Body Composition / physiology
  • Calcium / physiology
  • Exercise / physiology*
  • Humans
  • In Vitro Techniques
  • Male
  • Muscle Contraction / physiology*
  • Muscle Fibers, Fast-Twitch / chemistry
  • Muscle Fibers, Fast-Twitch / physiology*
  • Muscle Fibers, Slow-Twitch / chemistry
  • Muscle Fibers, Slow-Twitch / physiology*
  • Muscle, Skeletal / chemistry
  • Muscle, Skeletal / physiology*
  • Myosins / analysis
  • Protein Isoforms / analysis
  • Stress, Mechanical


  • Protein Isoforms
  • Myosins
  • Calcium