I often lecture people on exercise, and I frequently mention how 150 minutes a week of “moderate” exercise can be just as healthy as 90 minutes of heavier exercise. But what’s the difference between light, moderate and heavy?

The American College of Sports Medicine (ACSM) defines exercise intensity in three ways: percentage of maximum heart rate, rate of perceived exertion, and METS (metabolic equivalents). This can be confusing, but I think heart rate is the easiest to grasp. The basic points are:

• Moderate activity is ~60% of maximum heart rate (MHR).
• “hard” exercise is ~80% MHR, and
• “very hard” is >90% MHR

How To Find Your Heart Rate

There are a lot of online calculators to help you figure out your target heart rates. Most use the same formula:

Maximum workout heart rate=
(220 – age – resting heart rate) X percent of maximum heart rate + resting heart rate.

For example, a 24-year old with 65 beats per minute resting pulse would have:

Moderate (60% max) goal: (220 – 24 – 65) X .60 + 65 = 144 beats per minute
Heavy (80% max) goal: (220 – 24 – 65) X .80 + 65 = 170 beats per minute

You can quickly find out your max rate and goals at many websites: my favorite is at runnersweb.com.

Other Formulas: METs

Many articles mention METs, which stands for “metabolic equivalents”. This is a bit too abstract for most, but the general rule of thumb is that moderate exercise = 4-6 METs. So, what is 4 METs? Here’s a nice table describing METs and exercise:

The Bottom Line

Everyone should figure out what heart rate counts as moderate activity. You need to:

• first count your resting pulse for one minute;
• then use an online calculator to see what equals 60% of your max heart rate: that pulse should be your minimum goal during exercise.

Everyone should be striving for at least moderate activity levels, 150 minutes a week. Biking daily as a commute, or brisk walks and dancing, may get some of you there without the need for gym memberships.