fast twitch type 2 muscles fast twitch type 2 muscles fast twitch type 2 muscles fast twitch muscle fibers slow or fast-twitch muscles muscle fiber test fast-twitch muscle fibers fast twitch type 2 muscles fast twitch type 2 muscles two categories fast twitch type 2 muscles fast twitch and slow twitch fast-twitch muscles muscle fibers fast twitch type 2 muscles fast twitch type 2 muscles What Are Fast- and Slow-Twitch Muscles? fast twitch type 2 muscles