This muscle fibre responds best to high intensity such as heavy weight or interval training Body Types. There are three different basic body types that may genetically govern how much you can actually gain. This is important to understand so that you can work within your limits. If not, you may set goals that will be difficult or impossible to achieve. Slow twitch muscle fibers predominate, which make the ectomorph a natural endurance athlete, such as runners and triathletes.
Weigh gain is most difficult for the ectomorph.
Endomorphs are large and wide boned, often barrel chested. They usually have a mix of slow and fast twitch muscles. They naturally hold a higher body fat percentage of the three types. Offensive linemen in pro football invariably are endomorphs. Mesomorphs has a strong muscular physique with shoulders being wider than hips.