That means these two are known as fast twitch muscles. But this, which has a low contraction speed, this is known as a slow twitch muscle. So once again, these are the muscles that are found predominantly in the back and the legs. Because these muscles are the muscles that have a low fatigue rate, they can be used to basically support our body to give it posture. Now, these are the muscles that are used in middle distance events. For example, if we're running, let's say 400 or 800 meters, these are the muscles that we're going to use.