Dr S.S. ReddyWe have seen that blood moves round and round and that is why it is called circulation. Blood is pumped out of the left heart, goes to all areas of the body and comes back to the right heart. From the right heart it is pumped into the lungs and comes back to the left heart.The heart is an amazing organ. From its left half blood is pumped at 150 mm pressure which drops to 120 mm in the arteries. This is what we measure as blood pressure. The arteries end in thin walled capillaries through which all the nutrients and oxygen O2 are fed into all tissues body cells and CO2 produced in energy reactions is absorbed back into the capillaries.From the end of the capillary veins - blood vessels that return the blood - start and collect all the blood pumped out from the left heart and convey it to the right heart. From the right heart the blood is pumped into both lungs at a pressure of 25 mm; this pressure is enough to make the blood go into the lungs which are very close to the heart.The blood loses the CO2 in the lungs and picks up oxygen and reaches the left heart from where it is pumped at 150 mm pressure to the entire body again.It is necessary for us to understand circulation because fitness consists of accelerating the flow of blood for a short period of time daily 20-30 minutes. It is generally done by exercise which makes the left heart pump faster and stronger in the high pressure area.It can also be done by making blood move faster in the returning low pressure area by the right heart system. This is achieved by exercising the respiratory system breathing.In a circle whether we accelerate the flow in the right side or the left side, the blood flow in the entire circle moves faster and achieves fitness in the body.This is a different and equally good way of keeping fit.