Being physically fit allows the body to function at peak capacity, with all systems functioning effectively, including circulation, respiration, circulation, digestion, elimination and neurological function. Being overweight or obese places strain upon the bones, the heart, the joints and often the digestive system functions less efficiently in obese persons due to the presence of toxins and/or poor diet. Lack of physical fitness may also mean the body's circulatory system is not working efficiently, since lack of exercise means less oxygen moving through the blood. The organs of elimination also function less efficiently when there is a lack of physical activity as well: the skin is an example of one of the organs of elimination that benefits from exercise. The body needs to perspire to eliminate toxins to help protect against infection, and lack of exercise usually means less opportunity to perspire. Exercise also helps regulate body temperature by temporarily raising it and then forcing the body to perspire to cool off, and the regulation of body temperature helps bolster immunity.