D Slow-Twitch Type I
Activities Marathons, distance running, swimming, cycling, power walking, endurance training. Muscle Fiber Size Small. Force Production Low .Resistance to Fatigue Slow.Contraction Speed Slow. Mitochondria High. Capillaries High. Myoglobin High.ATPase Level Low. Oxidative Capacity High
Slow-twitch muscle fibers support long distance endurance activities like marathon running, while fast-twitch muscle fibers support quick, powerful movements such as sprinting or weightlifting. Slow-twitch muscle fibers have high concentrations of mitochondria and myoglobin. Although they are smaller than the fast-twitch fibers, they are surrounded by more capillaries. This combination supports aerobic metabolism and fatigue resistance, particularly important for prolonged submaximal (aerobic) exercise activities. Type I fibers produce less force and are slower to produce maximal tension (lower myosin ATPase activity) compared to type II fibers. But they are able to maintain longer-term contractions, key for stabilization and postural control.Slow-twitch muscle fibers are fatigue resistant, and focused on sustained, smaller movements and postural control. They contain more mitochondria and myoglobin, and are aerobic in nature compared to fast-twitch fibers. Slow-twitch fibers are also sometimes called type I or red fibers because of their blood supply. Fast-twitch muscle fibersprovide bigger and more powerful forces, but for shorter durations and fatigue quickly. They are more anaerobic with less blood supply, hence they are sometimes referred to as white fibers or type II.
