Mitochondria are called the powerhouses of cells, but when you look more closely they are more like refineries. They are the ones that produce adenosine triphosphate from various nutrients in food, which in turn serves as an energy source for the cells. This adenosine triphosphate ensures that a muscle can move. The mitochondria are a separate part of the cell that is decreasing in its functional capacity. This means that the body has less "fuel" available. The good news: intermittent altitude training can be a sensible option for focusing on the mitochondria: mitochondria that are no longer efficient should be replaced by new ones.