Finally, it is important to appreciate that while the classification of skeletal muscle fibers into three distinct groups is a convenient way to group the functional properties of muscle fibers, each classification exhibits a wide range of contractile and biochemical properties. Indeed, the biochemical and contractile properties of type IIx, type IIa, and type I fibers represent a contin-uum. Further, an individual muscle fiber can exhibit the blended qualities of more than one single fiber type. For example, some fibers contain more than one type of myosin ATPase (e.g., fibers can contain both type I and , type Ila myosin ATPases, whereas others may possess both type Ila and type 11x myosin ATPases).