Depends on oxygen delivery and aerobic mechanisms. have very fast-acting myosin atpases and depend upon anaerobic metabolism during contraction. red fibers, the smallest of the fiber types. contain abundant amounts of glycogen. abundant in muscles used to maintain posture. a relatively high percentage are found in successful marathon runners. a. slow (oxidative), fatigue-resistant fibers b. fast (oxidative or glycolytic), fatigable fibers