How Apple Watch’s Activity app measures exercise time

MacDailyNews reader Bruce writes:

I have now used my Apple Watch Sport since Friday evening and have seen a few posts on the Apple Community about the Activity app not recording the correct amount of time that you exercise.

Right after receiving the watch, I went on the stationary bike and rode for some time. I thought the recording was neat but did not pay much attention. Saturday, I rode for about 32 minutes and the Fitness app told me I had completed the 30 minute ride. Great, then I looked at the Activity app and found it only recorded 18 minutes of exercising.

So I started to think about why could this be. I believe that Apple is really only recording the amount of time in the Activity app that you exercise when your heart rate is in the target range of 70%-85% of your maximum heart rate. Remember when you set up the dashboard? You entered your age, weight and height. Apple is pulling that information to determine where your target range is. For me, being 63, my maximum heart rate is 157 and the 70%-85% target range would be 110 to 134.

The Mayo Clinic says this is how to calculate your maximum and target ranges: If you’re aiming for a target heart rate of 70 to 85 percent, which is in the vigorous range, you would calculate it like this:
• Subtract your age from 220 to get your maximum heart rate.
• Multiple that number by 0.7 (70 percent) to determine the lower end of your target heart rate zone.
• Multiply your maximum heart rate by 0.85 (85 percent) to determine the upper end of your target heart rate zone.

That being said, I found that I reach a heart rate of 110 somewhere around 10 minutes after starting on the stationary bike. Therefore, the times I have exercised and completed is 30 minutes, but Apple said I only did about 20 minutes. This would be correct when subtracting the 10 minutes of “warm up” to get to the target heart rate range.

I would much rather the Activity app tell me: “You have exercised 30 minutes and have been in your target range 20 minutes. You have 10 more minutes to go, don’t stop now.” But, since I stopped exercising after 30 minutes total, I will have “wasted” 10 of those 30 minutes on the warm up. What I should really do is 10 more minutes while within the target heart rate range.

MacDailyNews Take: According to Apple: The Activity app’s “Move” ring shows how many active calories you’ve burned. The “Exercise” ring shows how many minutes of brisk activity you’ve done. The “Stand” ring shows how many times in the day you’ve stood for at least one minute per hour.

Apple’ definition of “brisk activity” sounds, like Bruce supposes above, to be based on your target heart rate zone. That seems to be how Apple measures exercise and it makes sense as Apple needs a trigger, such as the very valid target heart rate, to begin recording exercise within the Activity app. Apple’s website states that “Exercise” is “how many minutes of brisk activity you’ve completed towards a goal of 30 minutes. Every minute of movement that equals or exceeds a brisk walk, whether it’s working out or playing with your kids, counts toward your Exercise goal.”

We’ve contacted Apple and will add any information they provide to this article. If anyone has additional information, please let us know below.

5 Comments

  1. and so it begins…………….the “pro reviewers” are clowns……I will take the “man on the street” report anytime ….

    I’m sure Apple has someone doing analysis on the opinions garnered through social media so that the apps will simply be improved dramatically over time……….

    Where the hell is my UPS guy…………………?!

  2. That could explain why on Saturday it recorded my 2 h brisk walk with the dogs as exercise but not the walk for 1.5 hours at a more leisurely pace on Sunday.
    I would consider those both exercises and should be recorded.
    I will have to check the settings and see if it can be changed.

  3. I think the activity app looks at the accelerometer info more than heart rate. I went on a brisk 1 hour walk with my heart rate in my target range the majority of the time. I even used the workout app which showed my active calories to be high and my avg. heart rate to be on target. But my arm didn’t move much. The activity tracker credited me 12 minutes of exercise. Later that night while watching a movie, I shook my arm back and forth and with a heart rate at near resting levels I racked up another 18 minutes of “exercise” by the activity tracker standard.

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