A mother sprints across the yard to grab her small child before he enters the street. The mother is using what kind of fibers

If you are learning about fast-twitch vs slow-twitch muscle fibers, then the answer would be fast-twitch muscle fibers. Fast-twitch muscle fibers are fibers used for powerful bursts of speed like sprinting, while slow-twitch muscle fibers are used for endurance-based activities like cross country running or marathons.