Fast-twitch and slow-twitch muscle fibers differ in their function and physiology. Fast-twitch fibers are designed for short bursts of explosive strength and power but fatigue quickly, making them ideal for activities like sprinting. In contrast, slow-twitch fibers are more resistant to fatigue and are suited for prolonged activities like distance running. They primarily rely on aerobic metabolism, which uses oxygen for energy. Understanding the differences between these fiber types can help athletes tailor their training regimens to enhance performance in specific activities.