How the heart responds during exercise

calculate the cardiac output by using a simple formula:Stroke Volume x Heart Rate = Cardiac Outputor(SV x HR= CO)Heart rate varies according to the amount of exercise you are doing. When you are sleeping deeply, your heart rate drops to a very slow rate to give the heart time to rest. When you are exercising hard, your heart rate can go up as much as almost three times its resting rate-but not for very long!The following equations are examples of how cardiac output is worked out:Average resting heart rate:70ml (SV) x 72 bpm (an average resting HR)= 5040 ml/minute or 5.04 litres per minute.If you raise the heart rate to 180 bpm through intensive exercise:70ml x 180bpm = 12,600 ml/minute or 12.6 litres per minute.That's like pushing six big bottles of soda through an organ the size of your fist every minute!Your heart would not be able to maintain this level of activity for a long time. So how do athletes train their hearts to work extraordinarily hard without them packing in?When the heart is exercised regularly it becomes larger and the volume of the chambers increases, as does the stroke volume. The heart of a trained athlete can pump more blood, and therefore more oxygen and nutrients, to the working muscles in the body each time the ventricles contract. So each beat of the heart pumps more blood than the average person, because the heart is larger.Therefore, it will require less effort by the heart to do ordinary things like walking up a flight of stairs or running for the bus. Just like a weight lifter uses less effort to lift 50kg than an average person does, the heart can pump more blood at a slower rate when demands are made upon it.So, going back to the formula, if the stroke volume has increased to 100ml, the amount of blood pumped (the cardiac output) will be higher even with a slower heart rate.100ml x 55bpm = 5500ml/minute or 5.5 litres per minute.An average person with a stroke volume of 70ml would have to raise his/her heart rate to 79bpm to pump the same amount of blood. That doesn't seem like a big difference, but if you were running a marathon you would want your heart working as efficiently as possible to go the distance!How to work out maximum heart rateIf you want to increase the fitness of your heart, it will take regular exercise. It is important to exercise at the right level to make the heart stronger without working it and yourself too hard. After all, different people have different boundaries - the heart of a 70 year old person will generally be less strong than the heart of a 20 year old person!There's usually a formula for everything, and this is no exception! Your maximum HR should be 220 - (your age). But working at your maximum heart rate all the time would tire your heart out very quickly. Therefore, your training rate or Target Heart Rate (THR) should be 75% of your maximum HR.So for a 15 year old person:220- 15 = 205bpm (max HR)75% of 205 = 154bpm (THR)So 154bpm would be the Target Heart Rate to maintain during your aerobic workout, after a warm-up. To get the best results, you should do aerobic exercise to raise your heart rate to this level for at least 20 minutes, three times a week. Aerobic exercise includes things like swimming, running, cycling, playing football or basketball, or dancing.