Ultrastructural Differences in Human Skeletal Muscle Fiber Types

The differences in type I and type II muscle fibers are further emphasized by ultrastructural studies. Type I fibers have features consistent with their predominant activity pattern, that is, endurance activity associated with aerobic metabolism. Type II fibers have features that emphasize their contribution to activity with greater dependence on anaerobic metabolism. These differences in features underscore the necessity of specificity in exercise and rehabilitation.