Aerobic & anaerobic enzymes – Increases in size and number of mitochondria are accompanied by increases in the enzymes that work inside to increase the production of aerobic energy. These changes explain increased performances in aerobic exercise. The same can be said of enzymes that help produce energy within the Lactic acid system when glucose is being broken down.
Fat - Fat is a main source of energy during low intensity exercise. When glycogen stores deplete during long periods of exercise the use of fat as a fuel increases. Trained athletes can use a greater amount of fat as a fuel compared to non-athletes which can help in preserving glycogen stores for a longer period.
Glycogen stores – These increase within the muscles cell and can then lead to increased duration / speed of performance.