The slow twitch muscle fibers are more efficient at using oxygen to generate more adenosine triphosphate (ATP) fuel for continuous, extended muscle contractions over a long time. They fire more slowly than fast twitch fibers and can go for a long time before they fatigue.
Slow twitch muscle fibers are good for endurance activities like long distance running or cycling.
Slow-twitch muscle fibers rely on the aerobic energy system. The aerobic energy system can be further divided based on the predominant fuel source. In aerobic glycolysis, carbohydrate sources are the primary source of fuel. This track of the aerobic system is used in events such as running a 5k or 8k. In events of longer duration such as a marathon, aerobic lipolysis – body fat, is the primary fuel source.