How should I set my heart rate zones?
November 5, 2021 1:14 PM   Subscribe

I have a Fitbit Charge 5, and it gives me Active Zone Minutes every day, and I greatly enjoy them. I am finding Active Zone Minutes way more motivating than steps. But I don't think its view of what constitutes activity reflects my actual body. Can you help me figure out where my zones should be? Or maybe they're fine where they are?

I am pretty fat and out of shape -- but improving! Just walking up a hill will have me panting and wheezing within half a block or so -- but that's an improvement over not being able to walk up a hill at all!

It seems clear to me that this is cardio -- but Fitbit will only sometimes give me a bit of cardio credit for the very top of the hill. My much smaller and much more fit mother, on the other hand, who doesn't even slightly breathe hard while we're walking together, gets lots of cardio minutes for the same hill at the same pace because she is older than me so her heart reserve is lower.

According to the explanatory text, Fitbit sets my active zones based on my heart rate reserve. Heart rate reserve is calculated as (220 - your age) - (your resting heart rate). I am 44 and my resting heart rate varies a little from day to day, but is basically 58ish. So my heart rate reserve is 118bpm.
Then it uses a percentage of heart rate reserve to calculate fat burn and cardio zones.
Resting heart rate + .4*heart rate reserve = fat burn zone. For me, around 105bpm
Resting heart rate + .6*heart rate reserve = cardio zone. For me, around 129bpm
Resting heart rate + .86*heart rate reserve = peak zone. For me around 158bpm

I am sure these very fine numbers have a scientific basis, but they just feel really wrong to me. How can I be panting and wheezing but that's not cardio? Fitbit lets you change either your max heart rate (220 - your age by default) or each zone individually to different training zones, and I would like to do that to better reflect my actual experiences, but what numbers do I set them to? Is there a fudge factor I can apply based on weight? Or a way to determine my actual max heart rate from Fitbit data?
posted by jacquilynne to Health & Fitness (8 answers total) 1 user marked this as a favorite
 
The results of this study indicate that the Tanaka et al. (14) MHR prediction equation (208 − 0.7 × age) was the best predictor of the actual MHR achieved during a maximal exercise stress test in this cohort. Importantly, this was found independent of gender, age or severity of overweight/obesity. Based on these findings, it is recommended that the Tanaka et al. equation (14) be used to establish MHR in individuals who are overweight or obese for the purpose of prescribing an aerobic exercise program, which is both safe and effective.

from here.

i did not read the whole thing, but it seems to be what you're looking for.

edit: well, shoot. that article is about maximum heart rate, not exactly what you're looking for. but maybe it will give you a starting point.
posted by misanthropicsarah at 1:21 PM on November 5, 2021


Response by poster: Maximum heart rate is one of the things I can reset, so that is helpful. But that formula doesn't come up with a much different result (177.2) than 220 - 44 (176), so it doesn't really change the zones, unfortunately.
posted by jacquilynne at 1:36 PM on November 5, 2021


Best answer: The Gulati formula is specific to women https://www.verywellfit.com/womens-heart-rate-response-exercise-3976885

Gulati's formula: 206 minus (0.88 * age) = MHR

I used it with my Fitbit to set active zones and got results that better matched my effort level.
posted by congen at 2:08 PM on November 5, 2021 [1 favorite]


But you may also want to discuss your resting heart rate with your doctor. Unless you’re very athletic, it’s unusual to have a RHR of 58 and could be a sign of problems https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/bradycardia--slow-heart-rate
posted by congen at 2:17 PM on November 5, 2021 [2 favorites]


Max heart rate is not generally regarded as a useful metric, and the 220-age formula is especially suspect (I've also seen 226-age for women specifically).

There is a different number, sometimes referred to simply as "threshold," more technically referred to as ventilatory threshold 2 (VT2). This is the heart rate you achieve in a sustained (at least, say, 4 minutes), very hard effort where your breathing is uncontrollable panting. It's pretty close to max HR, but not all the way there (by way of reference, for me, the max HR I've recorded in the past year is 172, and my VT2 is about 155–158). This is often considered a better baseline for setting zones.

The table on this page is confusing, but you can see the three zones (which I think are set the same as Fitbit's three) in the left column, and you can see %THR in the second-rightmost, so you could work out your zone breakpoints that way once you find your threshold.
posted by adamrice at 2:43 PM on November 5, 2021


Response by poster: The numbers that I get from fitbit after switching to my Gulati formula result look much more realistic. I will try those for a week or two and see how it feels.
posted by jacquilynne at 4:14 PM on November 5, 2021


Your FitBit is just for you--I recommend setting your hr zones empirically based on what is most useful for you. In particular, I was jogging without a heart rate monitor and able to push myself but miserable after and looking for any excuse to avoid it, then I started jogging with a hr monitor and set my goals to a point where I am working but not miserable and now I enjoy it and I'm actually getting faster/better/more stamina.

You can probably do this by just paying attention, cardio should feel like effort but also something you could keep doing for a while without keeling over. The point where you wouldn't feel like you were working if you went slower is the bottom, the point where you would have to stop pretty quickly if you went faster is the top. You will probably have to adjust a bit as you gain fitness, but also you will find that you need to go faster to get the same intensity.
posted by anaelith at 5:31 PM on November 5, 2021


I am sure these very fine numbers have a scientific basis

I don't think so -- mostly because I've not seen my max.HR drop over 10 years. In there studies height and the longest loop of the pressure wave from head to toe doesn't come up, so they're not using a model of compression/rarefaction bounded bytrying to fill a ventricle against the low pressure phase of the previous heart beat.

Most importantly, they weren't measured for you.

Check online for Rate of Perceived Exertion numbers to match bodily sensation to your sense of effort.
posted by k3ninho at 12:13 PM on November 6, 2021 [1 favorite]


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