You'll need help from a doctor or physiologist to calculate your exact MHR.
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When it comes to the average heart rate for exercise, it's important to recognize that there's no magic number that is going to work for everyone. Your age, fitness level and the intensity at which you exercise all play a role in how fast your heart will beat during a workout. As such, never compare yourself to others.
Age and Maximum Heart Rate
Your maximum heart rate, or MHR, represents the maximum number of times your heart can beat in a minute. As you age, your MHR decreases. While there are many ways to calculate MHR, the most basic way is to subtract your age from 220. By that calculation it's easy to see that a 20-year-old's maximum heart rate of 200 is far higher than a 50-year-old's MHR of 170.
Target Heart Rates
When you're exercising, the goal is to work out at a percentage of your MHR, called the "target" heart rates for exercise. For light exercise intensity, exercise at 40 to 50 percent of your MHR. For more moderate exercise intensity, work out at 50 to 70 percent, and for vigorous intensity, work out at 70 to 85 percent of your MHR. If you do the same type of exercise all the time, monitoring your heart rate can help you gauge whether you're exercising harder from one workout to another -- but again, don't compare your heart rate during a workout to those of your workout buddies or other people at the gym, even if you're doing the same workout.
Even if you're doing the same workout at the same intensity as another person who is the same age, you may find that your heart rates vary widely. Your heart is a muscle like other muscles. As you get more fit, your body becomes adapted to exercise and your heart and lungs won't have to work as hard to do the work. Thus, the fitter you are, the more blood your heart can pump during each stroke, meaning it won't have to pump as many times to deliver oxygen-rich blood to your cells. For that reason, fitter people tend to have lower heart rates than sedentary people of the same age.
How You Feel
It's OK to monitor your heart rate throughout your workouts -- but keep in mind that your heart rate can fluctuate for any of the reasons named above. It's best to use it as just one of a couple factors to monitor your workout. How you feel is equally important -- if not more important, reminds MayoClinic.com. If you feel like you're working out really hard, you probably are. Also factor in the length of your workout. If you're hoping to exercise for a long period of time, such as running a marathon, for example, you probably can't sustain an exertion level that feels really intense for very long. In that case, it's probably best to slow down your pace and aim for a level of exertion that feels moderate or light.