Muscle fiber types can be broken down into two main types: slow twitch (Type I) muscle fibers and fast twitch (Type II) muscle fibers. Type II fibers can subsequently be broken down into two types: type IIA, which is referred to as "fast twitch oxidative glycolytic", and type IIX, which is referred to as "fast twitch glycolytic". Slow twitch fibers are referred to as "slow twitch oxidative". Type I fibers are characterized by low force/power/speed production and high endurance, Type IIX fibers are characterized by high force/power/speed production and low endurance, while Type IIA fall in between the two.