Strengthening your heart will enable you to achieve cardiovascular fitness. You are fit your heart rate drops at least 30 beats per minute during the first 60 seconds after a maximum effort lasting at least five minutes. This decrement is called the recovery pulse rate. In order to calculate the decline precisely , you must measure your pulse during only the first five seconds after stopping the exercise, multiply this figure by 12, measure your pulse during a five second interval after one minute has passed, multiply this figure by 12, and subtract the second number from the first. You can’t determine your instantaneous heart rate at the conclusion of exercise by counting for an entire minute, since your heart rate will be much slower at the end of that minute than it was at the start. That is why you have to multiply the number of beats in the first five seconds by 12 and the number in the last five seconds by 12. (There are 12 five –second intervals in each minute.)
As you become more fit, your heart rate will return to normal sooner after you’ve finished exercising. This happen because your muscles will have increased amounts of enzymes which enable them to remove lactic acid, the breakdown product resulting from an oxygen deficit. As you become more fit , you should be able to exercise at any level more easily and can exercise at higher levels than you could before.