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