Normal levels of creatinine in the blood are approximately 0.6 to 1.2 milligrams (mg) per deciliter (dL) in adult males and 0.5 to 1.1 milligrams per deciliter in adult females. Muscular young or middle-aged adults may have more creatinine in their blood than the norm for the general population.
Types of muscle fibers. Skeletal muscle, the type that is responsible for moving our muscles when we run, is comprised of three different muscle fiber types, each with its own advantages, disadvantages, and specialty.
Skeletal muscles are divided into two muscle fiber types: 1  Slow-twitch (type I) muscle fibers contract more slowly and rely on aerobic metabolism. 2  Fast-twitch (type II) muscle fibers contract more rapidly due to the presence of a faster myosin.