Muscle glycogen stores and fatigue

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 Ca 2+ 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 Ca 2+ release during fatigue. This is consistent with compartmentalized energy turnover and distinctly localized glycogen pools being of key importance for SR Ca 2+ release and thereby affecting muscle contractility and fatigability.

Exercise-Induced Skeletal Muscle Remodeling and Metabolic Adaptation: Redox Signaling and Role of Autophagy

“…Skeletal muscle is the main storage site for glucose in the mammalian body. Glycogen is distributed in distinct localizations within the myofibers, depending on myofiber type and on training status (139). Lipids can also be stored as triglycerides in the myofiber, although excessive lipid accumulation is deleterious and might cause lipotoxicity and inflammation.…”

Evaluation of strength, agility and aerobic capacity in Brazilian football players

“…High VO 2max levels enhance the post-exercise recovery and utilization of the fat depot as an energy source. It is positive because it allows preservation of muscle glycogen stores [30]. Hence, football players with higher VO 2max levels are capable of running longer distances during a match and performing more sprints than those with lower VO 2max levels [22].…”

Molecular Basis for Exercise-Induced Fatigue: The Importance of Strictly Controlled Cellular Ca2+ Handling

“…Recent studies using electron microscopy imaging have shown that glycogen is preferentially located in three distinct subcellular compartments: subsarcolemmal, intermyofibrillar (i.e., between myofibrils), and intramyofibrillar (i.e., within the contracting myofibrils) (Marchand et al 2002;Nielsen et al 2009;Ørtenblad et al 2013). Although the exact role of the different pools of glycogen is not fully understood, electron microscopy images show a preferential depletion of intramyofibrillar glycogen in fatigued muscle fibers from rodents (Nielsen et al 2014(Nielsen et al , 2009) and humans (Marchand et al 2007;Nielsen et al 2011;Ørtenblad et al 2011).…”

“…These glycogen stores can become depleted during prolonged physical exercise (i.e., many minutes to a few hours) and there is strong correlation between glycogen depletion and fatigue-induced decline in exercise performance (Bergström et al 1967;Hermansen et al 1967;Ørtenblad et al 2013).…”