Fiber types (Type I, Type II)

Muscle fibers are classified into two main types based on their energy use and endurance. Type I fibers, also called slow-twitch fibers, are built for endurance and sustained activity; they burn fat efficiently and are fatigue-resistant, making them ideal for long exercises like marathon running. Type II fibers, or fast-twitch fibers, generate quick, powerful movements and rely more on carbohydrates, but they tire faster. They are further divided into Type IIa (more endurance) and Type IIb (more explosive). The mix of these fibers varies among individuals and influences athletic performance and muscle function.