Muscle glycogen stores and fatigue

Authors

  • Niels Ørtenblad,

    1. Institute of Sports Science and Clinical Biomechanics, SDU Muscle Research Cluster (SMRC), University of Southern Denmark, Campusvej 55, DK-5230 Odense, Denmark
    2. Swedish Winter Sports Research Centre, Department of Health Sciences, Mid Sweden University, Sweden
    Search for more papers by this author
  • Håkan Westerblad,

    1. Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77 Stockholm, Sweden
    Search for more papers by this author
  • Joachim Nielsen

    1. Institute of Sports Science and Clinical Biomechanics, SDU Muscle Research Cluster (SMRC), University of Southern Denmark, Campusvej 55, DK-5230 Odense, Denmark
    2. Swedish Winter Sports Research Centre, Department of Health Sciences, Mid Sweden University, Sweden
    Search for more papers by this author

  • This review was presented at The Journal of Physiology Symposium on Muscle metabolism and fatigue – in memory of Eric Hultman, which took place at the 15th International Biochemistry of Exercise Conference (IBEC), Stockholm, Sweden, on 18 June 2012. It was commissioned by the Editorial Board and reflects the views of the author.

N. Ørtenblad: Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, DK-5230 Odense M, Denmark. Email: nortenblad@health.sdu.dk

Abstract

Abstract  Studies performed at the beginning of the last century revealed the importance of carbohydrate as a fuel during exercise, and the importance of muscle glycogen on performance has subsequently been confirmed in numerous studies. However, the link between glycogen depletion and impaired muscle function during fatigue is not well understood and a direct cause-and-effect relationship between glycogen and muscle function remains to be established. The use of electron microscopy has revealed that glycogen is not homogeneously distributed in skeletal muscle fibres, but rather localized in distinct pools. Furthermore, each glycogen granule has its own metabolic machinery with glycolytic enzymes and regulating proteins. One pool of such glycogenolytic complexes is localized within the myofibrils in close contact with key proteins involved in the excitation–contraction coupling and Ca2+ release from the sarcoplasmic reticulum (SR). We and others have provided experimental evidence in favour of a direct role of decreased glycogen, localized within the myofibrils, for the reduction in SR Ca2+ release during fatigue. This is consistent with compartmentalized energy turnover and distinctly localized glycogen pools being of key importance for SR Ca2+ release and thereby affecting muscle contractility and fatigability.

Ancillary