Training-Induced Metabolic Adaptations in Skeletal Muscle.

Metabolism involves not only the conversion of nutrient fuel into usable energy but also includes the synthesis, modification, and exchange of cellular building blocks, acting as a regulator and sensor of cellular activities. Various components within metabolic pathways can affect cellular responses. A significant portion of daily energy intake is necessary for sustaining life, and physical activity demands are added to an intricately integrated machinery. Studying elite human performance offers valuable information about the molecular, cellular, tissue, and overall body adjustments to intense metabolic demands. Moreover, understanding the mechanisms and pathways activated during exercise could potentially uncover new therapeutic targets for prescription in patient populations.In this book chapter, we will review the structural and functional peculiarities of our skeletal muscle cells, the myofibers. After this brief introduction, we will also give an overview of skeletal muscle metabolism depending on the intensity of the exercise. The metabolic demands and regulation of very intense, intermittent, or "stop-and-go" sports and long-lasting exercise efforts will be reviewed. The main reasons to explain the importance of carbohydrates in supporting ATP production in high-intensity exercise and the downregulation of fat metabolism at high aerobic exercise intensities in athletes are also discussed. The last section of this book chapter is devoted to the main metabolic adaptations to cardiorespiratory and resistance exercise training. These include exercise-induced skeletal muscle fiber-type transitions, changes in capillaries and myoglobin, improvements in mitochondrial content and function, changes in glycogen and intramuscular triglyceride skeletal muscle stores, and improvements in tolerance for acid-base imbalances.