Mitochondrial bioenergetics of skeletal muscles

Abstract

Myofibril is the main contractile structure of a muscle; sarcomere is a functional unit comprising thin actin and thick myosin filaments. The process of muscular fiber shortening takes place through insertion of thin actinic filaments in between the thick myosin ones. The whole process is regulated by regulatory proteins troponin and tropomyosin. Energy necessary for muscle contraction is obtained from adenosinetriphosphate (ATP) produced in mitochondria. Energy necessary for ATP resynthesis is obtained by cleavage of phosphocreatine (PCr), carbohydrates, fats and proteins. During the aerobic ATP production, the majority of received oxygen is reduced by hydrogen to water. However a part of oxygen which is not reduced completely produces the so-called free oxygen radicals-univalent oxygen forms escaping from the transport chain. Production of oxygen radicals and their highly reactive derivatives, the so-called reactive oxygen species, increases during endurance exercise and may negatively affect the function of muscles and accelerate the process of fatigue. Exercise can cause imbalance between the levels of oxidants and antioxidants. This state, so-called oxidative stress, causes damage to enzymes, protein receptors, lipid membranes and DNA. On the other hand, exercise positively affects oxidative stress reduction and improves the function of mitochondria. Results of human studies are however frequently inconclusive. The antioxidative defense systemdepends on the intake of antioxidative vitamins and minerals with the diet (vitamins C, E, β-carotene and selenium), as well as on endogenous production of other substances with antioxidative effects (such as glutathione, coenzyme Q10) and of enzymes (such as superoxide dismutase), whose task it is to suppress free radicals. In most cases, antioxidant supplementation is unnecessary. The question whether supplementation with vitamins and other antioxidants increases sports performance and facilitates regeneration has not yet been explicitly answered. © 2008 Springer Netherlands.