Why do you put warm water over cramped feet?
Adding warm water improves blood circulation around the affected area.
During heavy exercises muscle cells respire anaerobically. Because there is not enough oxygen supply to these cells they breakdown glucose into lactic acid. The accumulation of lactic acid leads to cramps.
Heat dilates the blood vessel, thereby increasing the blood circulation around the sore area. As a result, the supply of oxygen and glucose also increases to these cells and leads to the complete breakdown lactic acid relieving the cramp.