How hard should you be working when you are working out? Are you wondering if you are working hard enough or too hard? There are many ways to measure your intensity, but the most common way is by measuring your hear rate. You can do this with various apps or watches or simply by palpating your pulse on our wrist or neck. In general, people usually try to keep their hear rate in a specific range based off their maximum heart rate. The most common way to estimate heart rate intensity is to take 220 and subtract your age to get your maximum heart rate, and then take a percentage of that number to get the best intensity for your workout. This method is ok- not great. Everyone’s resting heart rate is variable, usually anywhere between 60-80 beats per minute (bpm). Thus, it makes sense to factor in your resting heart rate to the calculation.

Heart rate reserve; What it is.

The Karvonen formula, or heart rate reserve (HRR), takes into account your resting heart rate. This makes more sense because if your resting heart rate is usually higher than the average of 60-80 bpm, then it will not take much increase in effort to get to your working intensity. Conversely, if your resting heart rate is typically lower than 60 bpm, it will be harder to get to your appropriate intensity.

Here’s how it works: Start with 220 again but subtract your age, then subtract your resting heart rate. Multiply that number by the desired percentage of work intensity. Finally, add your resting heart rate back to get your heart rate range.

Formula and Example

Formula Target Heart Rate (THR) = [(max HR − resting HR) × %Intensity] + resting HR See the example

Example Say you are 40 years old and you want to work at 60% of your maximum heart rate and your resting heart rate is 55 beats per minute.

THR = 220-40=180, thus [(180-55)] x 0.60 + 55 = 130 bpm

60% is a relatively hard intensity- above a walk but closer to a jog.

How to measure intensity if your medicine effects your heart rate

Of course if you are taking any medication that affects your resting heart rate, like a beta blocker for example, then it will affect your exercising heart rate as well. In that case, you can use a rating of perceived exertion scale. In the clinic and in research you may have heard of the Borg scale as a way to rate exertion. This scale is from 6-20. See the image below. This scale closely correlates with exercise heart rate intensity, with “6” correlating to a resting heart rate of 60 bpm and “20” correlating with a max heart rate of 220 bpm. Just add a zero to the number on the chart to get an estimate of a working heart rate. I find this visual to be helpful.

If you want a better explanation of the RPE scale and how to use it, please see the video clip where I discuss RPE and heart rate with Dr. Rachael Cordina, an adult congenital cardiologist who does research on congenital heart disease and exercise. Dr. Cordina practices medicine at Royal Prince Albert Hospital in Sydney Australia. She and I collaborated on a presentation for the Cardiac Neurodevelopment Outcomes Collaborative virtual conference.

What is the minimum intensity at which you should work?

However you choose to measure your intensity, the important thing is to just move and stay consistent. The intensity you work at is determined by your fitness goals. In general however, and to meet the recommendations for health set forth by the American College of Sports Medicine and the US Department of Health and Human Services, you need moderate activity, which typically is an RPE of around 13 or a heart rate intensity of 40-85 %HHR; keeping in mind that any intensity over 60% HRR is considered vigorous, for 150 minutes each week.

If this content was helpful for you and you would like to add a tip, please visit my virtual tip jar!