Skeletal muscles are designed to adapt to a person’s lifestyle therefore muscle composition varies significantly from a person who participates in little to no exercise, a professional weight lifter and a marathon runner. Several muscle adaptations can be notable in as little as a month of training. Aerobic exercises or endurance exercises can lead to changes in mitochondria content, muscle capillarity, and myoglobin. Endurance exercises requires the body to utilize energy for a long period of time. Aerobic metabolism is the chief source to supply the energy or ATP for endurance exercise. Aerobic metabolism uses one glucose molecule that is converted into carbon dioxide and water to produces 39 ATP molecules using fat, protein and carbohydrates.