Biology / Unit 13 Bio 3123 short lesson, about 20 seconds
Slow-Twitch and Fast-Twitch Muscle Fibers
Captions available
The idea
Slow-twitch fibers contract gradually and resist fatigue using aerobic metabolism, while fast-twitch fibers contract quickly and forcefully but fatigue sooner, relying more on anaerobic metabolism.
In practice
A marathon runner's leg muscles favor slow-twitch fiber, while a sprinter's favor fast-twitch fiber.
Where people slip
Most muscles mix both fiber types — a single muscle is rarely composed of one type exclusively.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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