Muscular Endurance
Muscular endurance is very important for athletes and those who have to sustain a physical activity for long periods of time. It is determined by how well-developed are your slow twitch muscle fibers.
There are two main types of muscle fibers in your body: slow twitch, and fast twitch. Slow twitch muscle fibers cannot exert as much force as fast twitch, though it can sustain an effort over a much longer period of time.
Fast twitch muscle fibers can exert a great amount of force albeit very briefly. In another word, slow twitch equals endurance, while fast twitch equals strength.
Cross country running is a prime example which depends on muscular endurance. In fact, it is probably the best type of exercise for training muscular endurance, as it involves very little muscular strength or flexibility.

