Answer to Question #60370 in Human Anatomy and Physiology for Sanjukta Ghosh

Question

What is the difference between fast and slow muscles? Could you please jot down four points of differences.

Answer 1

1. The levels of myoglobin: high level in slow muscles (red fibers) and low level of myoglobin in fast (white) fibers. Myoglobin determines the sensitivity of muscle to lack of oxygen. Because of its great content in fast muscles, they may work for a prolonged lack of oxygen and are involved in the implementation of non-intensive work, while slow muscles does not have such opportunity.
2. The source of energy: aerobic (oxidation of fatty acids and carbohydrates) in a slow muscles and anaerobic (glycolysis) in fast ones. Glycolysis in fast fibers provides rapid flow of ATP because these fibers have high ATPase activity, rapid use and restocking of ATP.
3. Diameter of myofibrils. Red fibers (slow muscles) have a small diameter. White fibers have a much larger diameter and also contain a lot of glycogen molecules, but have fewer mitochondria.
4. The power of muscle contraction: small in slow muscles and significantly greater in fast muscles. Due to the formation of energy by glycolysis white fibers accumulate lactic acid that leads to muscle fatigue that is not characteristic of slow fibers.