Fast-twitch and slow-twitch muscle fibers are distinguished by their function and endurance. Fast-twitch fibers are designed for explosive strength and power, supporting quick bursts of speed but fatigue quickly. Conversely, slow-twitch fibers are more endurance-oriented, functioning efficiently over long periods while utilizing aerobic metabolism. Understanding the differences between these muscle types can help tailor training programs to meet specific goals, whether athletic performance or general fitness.