Our body operates at 37° C as long as the blood flow functions at a normal rate. The flow rate depends on temperature and pressure. It is highest in the body core (40cm/sec) and up to 1/1000 times lower (0,4mm/sec) when it finally reaches the most distant extremities (fingers, toes) and before it pushes back to the core. The blood has now reached its lowest speed, is the coldest and uses additional energy to keep flowing. This process can result in cold pain or even hypothermia (undercooling). At an outside temperature below 0° C, the hands and feet can reach levels as low as 28° C.