Understanding GARMIN Heart Rate Zones Part 1: %Max HR

Until recently, keeping my heart rate in Zone 2 during an easy run seemed like an almost impossible task. I just couldn’t run slow enough to do it and even the slightest uphill would push my heart rate into Zone 3. It was very frustrating.

This led me to do a deep dive into how GARMIN determines Heart Rate zones and how my heart rate zone settings affect my ability to execute a heart rate based training plan.

In the end I realized that the reason it was so hard to run in Zone 2 was that my Heart Rate Zones were not configured correctly for me…

So if you’re having trouble running in Zone 2, or executing Heart Rate based workout plans in general, you may want to take some time to determine whether or not your GARMIN’s current Heart Rate Zone configuration makes sense for you.

This is Part 1 of a 4 part series on configuring and using heart rate zones with GARMIN.

GARMIN offers three different methods for determining heart rate zones:

• % Maximum Heart Rate (%Max. HR)
• % Heart Rate Reserve (%HRR)
• % Lactate Threshold (%LTHR)

In this post we’ll take a look at the most commonly used method for configuring heart rate zones with GARMIN devices: % Maximum Heart Rate (%Max. HR)

What is %Max. HR ???

We all have a maximum heart rate. In other words, it’s the fastest our heart is physically capable of beating. With the “%Max. HR” method GARMIN determines our heart rate zones as percentages of our Maximum Heart Rate as follows:

• Zone 5 (Maximum) 90-100% of Maximum Heart Rate
• Zone 4 (Threshold) 80-90% of Maximum Heart Rate
• Zone 3 (Aerobic) 70-80% of Maximum Heart Rate
• Zone 2 (Easy) 60-70% of Maximum Heart Rate
• Zone 1 (Warm Up) 50-60% of Maximum Heart Rate

For a runner with a Maximum Heart Rate of 170 bpm (beats per minute) GARMIN would configure their Zones as follows:

• Zone 5 (Maximum) 153-170
• Zone 4 (Threshold) 136-153
• Zone 3 (Aerobic) 119-136
• Zone 2 (Easy) 102-119
• Zone 1 (Warm Up) 85-102

Unless you change it, this will be the default method that your GARMIN uses for determining your Heart Rate Zones.

The key component of this method is accurately determining your Maximum Heart Rate. If that number is wrong the entire Heart Rate Zone configuration will be skewed.

So how do you know what your maximum heart rate is?

By default GARMIN will calculate your Maximum Heart Rate algorithmically based on your performance after you’ve completed a few runs with your device. (You can override this calculation by manually entering your maximum heart rate into the User Profile setting on your watch)

Another commonly accepted method for determining maximum heart rate is to subtract your age from 220. So a 45 year old runner could estimate their maximum heart rate to be 175 bpm.

Pros and Cons of using %Max. HR

Pros:

• This approach is generally well accepted in the running world
• It’s simple to use and GARMIN will set it up automatically

Cons:

• My experience is that both the GARMIN algorithm and the 220 minus age methods of calculating maximum heart rate significantly underestimate most runners’ maximum heart rate resulting in their heart rate zones being set too low.
• Even with an accurate maximum heart rate setting the zones are still very conservative.

Taking myself as an example, the GARMIN algorithm estimates my maximum heart rate to be around 175 bpm and 220 less my age (55) would give me a max heart rate of 165 bpm.

Let’s look at how my zones would be configured based on these two numbers using %Max. HR…

Max HR of 175 bpm (calculated by GARMIN)

• Zone 5 (Maximum) 90-100% 158-175
• Zone 4 (Threshold) 80-90% 140-158
• Zone 3 (Aerobic) 70-80% 123-140
• Zone 2 (Easy) 60-70% 105-123
• Zone 1 (Warm Up) 50-60% 88-105

Max HR of 165 bpm (220-55)

• Zone 5 (Maximum) 90-100% 149-165
• Zone 4 (Threshold) 80-90% 132-149
• Zone 3 (Aerobic) 70-80% 116-132
• Zone 2 (Easy) 60-70% 99-116
• Zone 1 (Warm Up) 50-60% 83-99

This means I would need to keep my heart rate below 123 bpm for a Zone 2 run assuming a max HR of 175, and below 116 bpm assuming a maximum HR of 165. I know based on experience that keeping my HR below 123 would be very difficult and keeping it below 116 would be virtually impossible!

What’s wrong with the calculation?

For myself, the discrepancy is at least partly due to the fact that my maximum heart rate is actually much higher than either of these numbers. I was able to prove this by pushing myself to run as hard as possible up a steep hill at the end of a recent tempo run. Doing this I saw my heart rate reach 183 bpm before I got lazy and stopped.

Here’s how my zones would be configured based on a Maximum Heart Rate of 183 bpm:

• Zone 5 (Maximum) 90-100% 165-183
• Zone 4 (Threshold) 80-90% 146-165
• Zone 3 (Aerobic) 70-80% 128-146
• Zone 2 (Easy) 60-70% 110-128
• Zone 1 (Warm Up) 50-60% 92-110

Though this is slightly more manageable I would still find it very frustrating trying to run slow enough to keep my heart rate below 128 bpm on my easy runs.

Conclusions:

I suspect many GARMIN runners are likely using the default configuration of having GARMIN auto detect their maximum heart rate along with the default option of using %Max HR to automatically configure their heart rate zones resulting their Zone 2 being configured too low.

If you are finding it difficult or impossible to keep your heart rate in Zone 2 on your easy runs you may want to check to see how your Zones are currently configured (see my video on how to do this here).

Is it bad to use %Max HR to determine my HR Zones?

Not necessarily. While this approach may result in a configuration that doesn’t work for some runners that will not always be the case. If your heart rate while running at a comfortable pace and being able to hold a conversation falls within your Zone 2, that’s a sign your zones are configured correctly.

You can also browse your GARMIN statistics from the past several months or so to see what’s the highest heart rate you’ve recorded. Does it match the Maximum Heart Rate that GARMIN is using to calculate your zones? If so, this is another good sign.

In future posts we will take a similar look at the “% Heart Rate Reserve” and “% Lactate Threshold” methods of determining heart rate zones and then conclude with tips on how to determine which approach is best for you.