Muscle Fiber Types

Skeletal muscle comprises several different types of muscle cells. These cells differ in their rate of contraction and metabolic activities. This cross section of skeletal muscle was stained to label slow-twitch muscle fibers (type I). These cells express muscle myosin that has a slow ATPase rate and are adapted for long, slow contraction. The lighter staining muscle cells express muscle myosin that has a fast ATPase rate. These are fast-twitch muscles (type II) and the cells tend to be larger. Which type of muscle cell contains more mitochondria? Myoglobin? Glycogen?