Heart, Circulation, Respiration and Blood; Environmental and Exercise Physiology

Pflügers Archiv

, Volume 403, Issue 4, pp 369-376

First online:

Influences of endurance training on the ultrastructural composition of the different muscle fiber types in humans

  • Hans HowaldAffiliated withForschungsinstitut der Eidg. Turn- und Sportschule
  • , Hans HoppelerAffiliated withAnatomisches Institut der Universität Bern
  • , Helgard ClaassenAffiliated withAnatomisches Institut der Universität Bern
  • , Odile MathieuAffiliated withAnatomisches Institut der Universität Bern
  • , Reto StraubAffiliated withKlinik für Nutztiere und Pferde der Universität Bern

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To investigate changes in the ultrastructure of the different muscle fiber types induced by endurance training ten sedentary subjects (five women and five men) were exercised on bicycle ergometers 5 times a week for 30 min. After 6 weeks of training there were significant changes in\(\dot V_{{\text{O}}_{{\text{2max}}} } \) (+14%), in the percentage of type I (+12%) and type IIB fibers (−24%) as well as in the volume densities of mitochondria. The latter increased 35% in type I, 55% in type IIA and 35% in type IIB fibers. The relative increase in subsarcolemmal mitochondria was larger than in interfibrillar mitochondria in all fiber types. There was also a significant increase in the volume density of intracellular lipid in type II fibres. It is concluded that high intensity endurance training leads to an enhancement of the oxidative capacity in all muscle fiber types.

Key words

Mitochondria Intracellular lipid Electron microscopy Morphometry Histochemistry Muscle biopsy