Now let's move on to the type two A and type two B scale to muscle. These are known as fast twitching skeleton muscles because they actually contract quickly. Now just like type one, type two A also appear red under the microscope because they also have a high concentration of myoglobin. However, they actually break down ATP at a high rate and that's exactly why they contract quickly and that's exactly why we call them fast twitch fibers, fast twitch muscles. Now although they are still slow to fatigue, they have a low resistance to fatigue than our type one. So type one muscles are capable of resisting fatigue at a very high percentage while type two A basically resist fatigue at a lower rate than type one.