Regeneration refers to processes that lead to the recovery or renewal of depleted energy reserves and the restoration of a physiological balance in the body. Regeneration has a (re)supplying function and is significantly involved in our physical and mental fitness. After a phase of activity, during which metabolic byproducts such as lactate (produced through anaerobic sugar metabolism in the muscle) or ammonia (from protein metabolism) are formed, the body requires a recovery phase to transport and break down these byproducts from their site of production (for example, in the liver) or to excrete them through the kidneys or lungs. The body needs to be "cleaned up" or regenerated after periods of exertion. This means that metabolites must be broken down or excreted, shifts in electrolyte balance must be corrected, and energy reserves must be replenished to handle the next phase of activity. Various processes play an important role in restoring physiological balance, and many of these processes are interconnected.