"Fast-twitch" refers to a type of muscle fiber that contracts quickly and powerfully but fatigues rapidly. These fibers are essential for high-intensity activities like sprinting and weightlifting, where short bursts of energy are required. Fast-twitch fibers rely more on anaerobic metabolism, which means they generate energy without using oxygen. Athletes often have a higher proportion of fast-twitch fibers, which can enhance their performance in explosive sports. Training can influence the development of these fibers, with activities like plyometrics and sprints being particularly effective. Understanding fast-twitch fibers can help in designing targeted training programs for athletes.