Calculate Target Heart Rate

Step One

Use the following formula to calculate your maximum heart rate:
Maximum heart rate = 220 - your age.
Thus, for a 20 year old person, the maximum heart rate is 220-20= 200.

Step Two

Your target heart rate is 65% to 85% of your maximum heart rate.
Thus, for a 20 year old, the target heart rate is between 65% to 85% of the maximum heart rate of 200.
65% of 200 = 130
85% of 200 = 170
Therefore, to get the most benefits out of physical activity, a 20 year old must maintain their heart rate between 130 beats per minute to 170 beats per minute.

Step Three

Now that you know how to calculate your target heart rate, you need to check your pulse while exercising to ensure you are withing the target heart rate. If you want to learn how to check your pulse, please see the article below:

http://www.bukisa.com/articles/38500_how-to-take-pulse

Step Four

If checking the pulse during exercise is inconvenient, consider buying a heart rate monitor such as the Polar heart rate monitor, which will automatically calculate your heart rate for you as you exercise.

Step Five

Another quick rule of thumb way of knowing that you are exercising within your target heart rate (this is not 100% accurate) is that your exercise should be light enough that you can speak, but heavy enough that you cannot sing during it.