Creatine occurs naturally in the livers of human beings and is called upon to increase skeletal muscular contractions without tiring as quickly and to improve cellular oxygen uptake. When the natural reserves are depleted, the body will automatically pull creatine from the bloodstream in order for the body to continue the activity. Should the person ingest a dose of creatine and do nothing physically active that requires stressful amounts of muscle contraction, the body will convert the extra creatine into creatinine, the antithesis of creatine, and excrete it through the urine in under an hour.