HR Zones off due to a Threshold HR estimate that’s too high?

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    I’m beginning to suspect that I’ve been training with my zones set incorrectly by having a threshold heart rate estimate that’s too high. I could use some advice and input.

    I’ll start by saying that I’ve defaulted to the value my Garmin watch has given me. I have the Garmin Forerunner 955; previously, I had the 945 and 245 (I mention this because they/I have years of collected data). Garmin occasionally changes the estimated value, but it has stayed pretty constant for the most part. My threshold HR from Garmin is estimated at 169.

    I’ve used that value in TrainingPeaks and the 80/20 calculators to calculate heart rate zones and followed them religiously. (At least, to the best of my ability.)

    I’m in Week 10 of the “80/20 Running: 2023 Edition Ultra 50 Kilometer Level 3” training plan. Training is going well, but I’ve started to feel … very fatigued.

    I started thinking my zones were off when I started doing the interval workouts. Despite hitting the pace zones, I could never get my heart rate into zones 4 or 5. Even though I felt I was giving it my all for some of the Zone 5 intervals, my heart rate would hardly get into Zone Y. I’ve never seen it hit Zone 5 as defined by a threshold HR of 169.

    I’ve dug around and have reason to think it’s too high. For example, I ran a 5K race about 10 weeks ago. I read that you can take the average heart rate of a 5K race and subtract 15 from it to get a reasonable estimate. If I do that, I get 159; that’s 10 lower than what Garmin tells me. And when I apply 159 to 80/20 zones, I see a big difference.

    I’m tempted to restructure my zones based on 159 and see how it feels.

    I’d love input. While I’ve been running for years, it’s only recently I’ve started to take things more seriously. I am concerned, despite attempts to the contrary, I’m running too hard too often.

    Thank you!

    • This topic was modified 7 months, 3 weeks ago by WadeWegner. Reason: typo

    I would recommend doing a 20 minute fitness test during your next recovery week. That will allow you to know for sure what your threshold is.

    The heart rate not getting into zone 4 or 5 during an interval is not unusual due to lag. The efforts are usually too short for the heart to get that high.

    Also how’s your nutrition? Are you eating enough carbs? If you aren’t fueling properly, your body will let you know by being tired.

    For a comparison, I’m currently in week 13 of a level 3 marathon plan. I need to consume between 7-8 grams of carbs per kg of body weight a day. I generally weigh my food to ensure I’m getting enough carbs. Last week I wasn’t consistent in measuring and I know I was short on carbs as I felt fatigued. This week back to measuring and getting enough and feeling great again.



    You could use the data from your most recent 5k as you mentioned above and reset your zones using those numbers. If you are struggling with keeping up with the zones, I dont think theres any harm in dropping them just a bit using the new data.

    As Andrew mentioned above, make sure you are fueling well, hydrating well and recovering properly. These may also be contributing to your overall fatigue.

    Let me know if you have any more questions!

    Coach Anne


    Thank you, Andrew and Anne! I appreciate you both.

    I decided (for now) to go with the new zones based on the 5K methodology. That, plus a rest day, seems to have me back on track. I did an 18-mile run today (ER17, Endurance Run) in the new Zone 2, and it felt pretty good.

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