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.
The fast-twitch muscle fibers are those that have less endurance but have the most strength and power and grow the biggest. When you pick up a weight and do a biceps curl, the slow-twitch muscle fibers in the biceps are recruited first to contract and then lift the weight.