Low and Medium Intensity Exercise, Defined

In a previous posting, I offhandedly used the terms �low intensity� and �medium intensity� aerobic activity. Perhaps you�re already familiar with these terms, though I think for many people these terms are about as meaningful as Urdvha Dhanurasana or other Sanskrit names.

While �low intensity aerobic activity� may sound pretty technical, I think most of us have an intuitive, seat-of-the-pants understanding of what a low intensity or medium intensity workout may feel like. Unfortunately, these terms are largely relative. By whose standard? By the standards of the marathon runner? Or the devout couch potato?

Thankfully, we can quantify these terms by keeping tabs on our heart rate. In keeping track of our heart rate, we can find the just-right challenge for each person, regardless of whether they�re an elite athlete or just starting to get back in shape.

We all have a maximum heart rate. The harder we work out, the faster our heart beats� to a certain point. For each of us, our heart will only beat so fast.  This maximum heart rate varies from person to person, though scientists have found some reliable patterns. Firstly, maximum heart rate tends to correlate strongly to age. Secondly, most people�s maximum heart rate is no more than about 220 beats per minute.

After years of studying thousands of people, scientists found that if you subtracted a person�s age in years (human years, not cat or dog years) from 220, you arrive at a pretty good approximation of their maximum heart rate.

220 – age (in years) = calculated Maximum Heart Rate (MHR)

For example, I�m 48 years old. Subtracting 48 from 220, I end up with a calculated maximum heart rate of 172 beats per minute. While this isn�t exactly my maximum heart rate (more on that in a forthcoming post), it�s sufficiently close for the purpose of monitoring the intensity of my workouts.

OK, now what do you do with this esteemed MHR number? With the MHR number in hand, we can now quantifiably define what�s meant by low-intensity or medium-intensity aerobic exercise.

Low intensity aerobic exercise is commonly defined by a heart rate that�s 55-65% of MHR. Medium intensity aerobic exercise is commonly defined by a heart rate that�s 65-75% of MHR.

In my body, I�m just starting to derive the aerobic benefits of working out when I�m in the low intensity zone of 95-112 beats per minute (BPM). I�m in medium intensity zone when my heart rate is between 122-129 BPM.

To develop heart-healthy fitness, I�ve been enjoying activities with my heart rate in the 95 to 129 BPM range.

By keeping my heart rate in this low to moderate intensity zone, I�ve enjoyed 90+ consecutive days with 30+ minutes of aerobic activity. It�s felt great, and I can almost feel how my body is growing stronger and healthier.

What is your calculated maximum heart rate? What is 55-75% of your MHR? What would it feel like to spend 200-minutes in this zone each week?

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