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.
Each myocyte contains many myofibrils, which are strands of proteins (actin and myosin) that can grab on to each other and pull. 1  This shortens the muscle and causes muscle contraction. 2  Therefore, slow twitch fibers are great at helping athletes run marathons and bicycle for hours.