Energy metabolism in different skeletal muscles and muscle fibers: implications for injury and dietary supplementation.

The necessary energy supply in skeletal muscles is based on either glycolysis or mitochondrial oxidative phosphorylation (OxPhos). These two bioenergetic pathways are in balanced complementation. Glycolysis is faster than OxPhos, whereas OxPhos is much more efficient. One common feature of both pathways is the compartmentation of high-energy phosphates and their metabolic channeling. The glycolytic muscles are wider, whereas oxidative muscles have significantly more mitochondria. Importantly, a striking difference in bioenergetic mechanisms in oxidative (slow-twitch) versus glycolytic (fast-twitch) muscles and muscle fibers has been clearly shown. The advantage is that the optimal fiber diversity can provide the best muscle function. Various creatine kinase isoforms and phosphocreatine play an important role in glycolytic and oxidative muscles energy metabolism, but their roles are very different, depending on the muscle type. In the glycolytic muscles, phosphocreatine, produced from creatine and ATP by cytosolic creatine kinase, is mostly considered a cellular energy store for fast ATP delivery, whereas in the oxidative muscles, phosphocreatine and mitochondrial creatine kinase are the main players in the intracellular energy transport.