That means we can use them for hours and hours before they actually run out of that fuel source. So we can continually use our fats as our major storage fuel to form ATP. And that's exactly why these are the muscles that are used when we carry out very long activities such as running a marathon. So if we're running a marathon, that basically means we have to use muscles that will not fatigue very quickly. And that's why we use the type one muscles. Now, these are the muscles that also have a relatively low diameter.