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.
Muscle Fibers Do Different Things. Your skeletal musclesâthe ones you check out in the mirrorâhave two main types of fibers. Type I fibers, also called slow-twitch, are used mainly for endurance activities. Type II, or fast-twitch, begin to work when a task utilizes more than 25 percent of your maximum strength.