The "target heart rate" is very important when you want to know how to do your exercise properly <em>without straining your body</em> <em>or relaxing too much. </em>In order to do this, you have to get your<em> "maximum heart rate"</em> first by subtracting your age from 220. The difference will be multiplied by 60% to 85%, depending on the exertion level that you want.
For example, your age is<em> 20</em>. You have to<em> subtract 20 from 220 </em>and that will give you a maximum heart rate of <em>200 beats per minute (bpm).</em> If you want a 60% exertion level, your target heart rate is 120 bpm (200 x 60%).