Are Skeletal Muscles White or Red?

Yes! There are three kinds of muscle: cardiac, visceral (involuntary) and skeletal (voluntary). Skeletal muscles that you use to lift weights in the gym are made up of white and red muscle fiber. How much of each type of muscle fiber we have is genetic.

Thus red muscle tissue contains an extra chemical a special protein-type molecule for oxygen storage called myoglobin. This molecule gives the muscles their red color. The presence of myoglobin in posture muscles enables the sustained contractions for maintaining proper posture and walk. Muscles that depend predominantly on oxidative phosphorylation for ATP require abundant oxygen. Oxygen in these muscles is stored as oxymyoglobin. These muscles are glycolytic, lack appreciable myoglobin and appear white. These muscles generally generate most of their ATP from glycolytic reactions. White fibers generate ATP by a short reaction pathway between substrates such as glucose and the appearance of ATP, whereas in red muscle the pathway from substrate such as glucose to ATP is comprised of many more reaction steps and and is a longer process.

Fast-acting skeletal muscles such as those used by power lifters are composed of dominantly glycolytic white fibers while slow-acting muscles such as those that maintain tone or that are used for marathon running are generally red and oxidative. Most of us have an intermediate balance of white and red muscle fibers. Other people like those that are top marathon runner or power lifters have a predominance of one type of muscle fiber. Most likely, an avid marathon runner could not power life and an avid power lifter could not run a marathon!

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