Gauging intensity using your heart rate

Another way to gauge your exercise intensity is to see how hard your heart is beating during physical activity. To use this method, you first have to figure out your maximum heart rate — the upper limit of what your cardiovascular system can handle during physical activity.

You can calculate your maximum heart rate by subtracting your age from 220. For example, if you're 45 years old, subtract 45 from 220 to get a maximum heart rate of 175. This is the average maximum number of times your heart should beat per minute during exercise.

Once you know your maximum heart rate, you can calculate your desired target heart rate zone — the level at which your heart is being exercised and conditioned but not overworked.

The American Heart Association generally recommends a target heart rate of:

• Moderate exercise intensity: 50% to about 70% of your maximum heart rate
• Vigorous exercise intensity: 70% to about 85% of your maximum heart rate

If you're not fit or you're just beginning an exercise program, aim for the lower end of your target heart rate zone. Then, gradually build up the intensity. If you're healthy and want to exercise at a vigorous intensity, opt for the higher end of the zone.

How to determine your target heart rate zone

Use an online calculator to determine your desired target heart rate zone. Or, here's a simple way to do the math yourself. If you're aiming for a target heart rate in the vigorous range of 70% to 85%, you can use the heart rate reserve (HRR) method to calculate it like this:

• Subtract your age from 220 to get your maximum heart rate.
• Calculate your resting heart rate by counting how many times your heart beats per minute when you are at rest, such as first thing in the morning. It's usually somewhere between 60 and 100 beats per minute for the average adult.
• Calculate your heart rate reserve (HRR) by subtracting your resting heart rate from your maximum heart rate.
• Multiply your HRR by 0.7 (70%). Add your resting heart rate to this number.
• Multiply your HRR by 0.85 (85%). Add your resting heart rate to this number.
• These two numbers are your average target heart rate zone for vigorous exercise intensity when using the HRR to calculate your heart rate. Your heart rate during vigorous exercise should generally be between these two numbers.

For example, say your age is 45 and you want to figure out your target heart rate zone for vigorous exercise using the HRR method. Follow these steps:

• First, subtract 45 from 220 to get 175 — this is your maximum heart rate.
• Next, check your resting heart rate first thing in the morning. Say it's 80 beats per minute. Calculate your HRR by subtracting 80 from 175. Your HRR is 95.
• Multiply 95 by 0.7 (70%) to get 66.5, then add your resting heart rate of 80 to get 146.5.
• Now multiply 95 by 0.85 (85%) to get 80.75, then add your resting heart rate of 80 to get 160.75.
• Your target heart rate zone for vigorous exercise is 146.5 to 160.75 beats per minute.

How to tell if you're in the zone

So how do you know if you're in your target heart rate zone? You can use an activity tracker to check your heart rate regularly while you exercise.

Or use these steps to check your heart rate during exercise:

• Stop briefly.
• Take your pulse for 15 seconds. To check your pulse over your carotid artery, place your index and third fingers on your neck to the side of your windpipe. To check your pulse at your wrist, place two fingers between the bone and the tendon over your radial artery — which is located on the thumb side of your wrist.
• Multiply this number by 4 to calculate your beats per minute.

Here's an example: You stop exercising and take your pulse for 15 seconds, getting 37 beats. Multiply 37 by 4, to get 148. If you're 45 years old, this puts you in the target heart rate zone for vigorous exercise, since the target zone for that age is between 146.5 and 160.75 beats per minute using the HRR method. If you're under or over your target heart rate zone, adjust your exercise intensity.

Target heart rate tips

It's important to note that maximum heart rate is only a guide. You may have a higher or lower maximum heart rate, sometimes by as much as 15 to 20 beats per minute. If you want a more specific range, consider discussing your target heart rate zone with an exercise physiologist or a personal trainer.

Generally only elite athletes are concerned about this level of precision. They may also use slightly different calculations that take into account sex differences in target heart rate zones. These differences are so small that most casual athletes don't need separate calculations for men and women.

Also note that several types of medications, including some medications to lower blood pressure, can lower your maximum heart rate, and then lower your target heart rate zone. Ask your doctor if you need to use a lower target heart rate zone because of any of your medications or medical conditions.

Interestingly, research shows that interval training, which includes short bouts (around 15 to 60 seconds) of higher intensity exercise alternated with longer, less strenuous exercise throughout your workout, is well tolerated. It's even safe for those with heart disease and type 2 diabetes. This type of training is also very effective at increasing your cardiovascular fitness and promoting weight loss.