understanding exercise intensity and how to measure it for optimum fitness level

Exercise intensity is shown in your breathing and heart rate, whether you're sweating, and how tired your muscles feel.

There are two basic ways to measure exercise intensity:

  • How you feel. Exercise intensity is a subjective measure of how hard physical activity feels to you while you're doing it — your perceived exertion.

  • Your heart rate. Your heart rate offers a more objective look at exercise intensity. In general, the higher your heart rate during physical activity, the higher the exercise intensity.

You can use either way of gauging exercise intensity. If you like technology, you can check your heart rate with an activity tracker.

Here are some clues to help you judge your exercise intensity.

Moderate exercise intensity

Moderate activity feels somewhat hard. Here are clues that your exercise intensity is at a moderate level:

  • Your breathing quickens, but you're not out of breath.

  • You develop a light sweat after about 10 minutes of activity.

  • You can carry on a conversation, but you can't sing.

Vigorous exercise intensity

Vigorous activity feels challenging. Here are clues that your exercise intensity is at a vigorous level:

  • Your breathing is deep and rapid.

  • You develop a sweat after only a few minutes of activity.

  • You can't say more than a few words without pausing for breath.

Overexerting yourself

Beware of pushing yourself too hard too often. If you are short of breath, are in pain or can't work out as long as you'd planned, your exercise intensity is probably higher than your fitness level allows. Back off a bit and build intensity gradually.

It’s important to know we're working hard enough that our heart is getting beneficial activity and beneficial exercise. That’s known as our Target Heart Rate (THR).

How do we measure our THR?

First you have to figure out your maximum heart rate — the upper limit of what your cardiovascular system can handle during physical activity.

Max heart rate = 220-age

For example if you're 45 years old, subtract 45 from 220 to get a maximum heart rate of 175.

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

How to determine your Target Heart Rate:

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.

Ideally, aim to spend at least 20-30 minutes of the one-hour exercise class within your target heart rate zone

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