The cardio readings on my Apple Watch are inconsistent

I was just as perplexed, but then I remembered a couple of things. First, cardiovascular monitoring, including recovery, output, and health, is a complex scientific measurement. No commercially available worn device (non-medical) can accurately replicate laboratory diagnostic testing. Laboratory testing monitors respiratory rate, heart rate, and blood pressure to calculate the efficiency of your cardio engine. Worn devices use metrics and data to feed an algorithm the developers create to estimate our bodies performance. The algorithms are predictive based on the metrics and data they use and therefore can only estimate, not truly measure. I use the numbers as a guide, but I base my fitness level more on how I feel and how I perform, not on what my watch and phone tell me.

The second part of this is, when you workout consistently over time, your body becomes more efficient and your total cardio output increases. Your heart begins to pump more blood in less beats (stronger heart contractions, better alveolar O2/CO2 transfer, better vascular tone). In other words, your maximum heart rate slows when your fitness level increases. Instead of having to beat 180 times per minute to meet oxygen demands at peak exercise levels, it may only beat 160 times per minute when your cardio fitness begins to peak. This means recovery beats are calculated from a lower peak heart rate. Again, focus more on how you feel and perform.

The last part of this is that the worn devices use averages and it takes time for those averages to adjust. If your VO2 max is below 33 for several weeks your device will tell you it is below average. The trend line will show your increases, but the average is going to show below average until you hit higher numbers for an extended period of time. Again, the device is not able to measure true body performance, they can only estimate. An example is the Apple Watch blood oxygen (SpO2) monitor. I have found when compared to a calibrated Pulse Oximeter, the measurements are, on average, 3 percent or more lower on the watch.

Just a quick update.

My cardio recovery kept dropping along with cardio fitness as I was getting fitter. My watch updated to 10.3.1 and cardio recovery is steadily getting higher. It originally was 42 then dropped to 24 then down to 21 and stayed in a straight line and wouldn't move from 21 for every run I did. Since the update it's steadily increased to 30.

Hi nikolina51,

As you are concerned about the accuracy of the readings from your Apple Watch, see if the steps in the following resources help:

• Get the most accurate measurements using your Apple Watch
• Calibrate your Apple Watch for improved Workout and Activity accuracy

If you continue to get inaccurate readings from your Apple Watch, contact Apple Support for further assistance: Get Support.

Take care.

I am seeing the same thing. My theory, and it is only that so far, is that “cardio recovery” is measuring how much your heart rate reduces after exercise, but on a delay - maybe starting a minute or two after the actual exercise ends. When you’re out of shape your heart rate is still quite high at that point, but as you get fitter you will have already recovered quite a bit, so the delta between your heart rate at that delayed point and your resting heart rate gets smaller.

If that is the case it would make sense, but I’m not sure what the logic behind measuring that way would be.

remember to stop workout tracker immediately after your max heart rate. In other words don’t record recovery, slow down or stretches after a run. If you do not stop the fitness trackers immediately it will under estimate your recovery.

say you run and peak heart rate was 150 and you stop running, immediately stop the app and just sit/rest and let HR drop. If you keep walking or cooldown, it will underestimate your recovery time.

I noticed the same thing in my health data as well, recovery dropping from the 40s down to the 20s. I just started using Apple Fitness+ in January, so my first theory was that maybe it was calculating the recovery rate from the end of the AF+ workouts, which generally have a minute or two of cooldown already baked into them. Meaning my heart rate had already recovered by the time the workout officially ended, so it was seeing a much smaller difference.

Then, when I drilled down into the data on my iPhone, I saw that it hadn't been collecting ANY heart rate recovery data since the end of December. No clue why it stopped collecting data or what I might do to fix it....

More recent studies validating the Cole et al. findings show that Cardio Recovery or heart rate recovery of 13 or greater (meaning a drop of 13 bpm or more) after 1 minute, or 22 or greater after two minutes is in the normal/healthy range.

Just thought I'd paste this in here as it can be quite worrying seeing some low numbers and thinking something's wrong. Perhaps we all rely on tech too much these days, just know that everyone here is doing the best thing for their health by exercising in the first place. I can only imagine Apple's code has since changed to be more "accurate" and it's not you that's getting worse!

I've gone from a consistent 43 for three weeks to 19 overnight, where it's remained for a week now.

Nothing's changed in terms of my health and fitness (same diet, same work outs, same everything).

When I go to Cardio Recovery>Show All Data, I can see that the data is being captured every few days. So over three weeks, I have 12 data points all logged as 43 (zero variation from this number). Then it's more than halved to 19 and remained there (ie: I now have 3 data points over a week all logged as 19).

The lack of fluctuation in the number being logged every few days plus the immediate and unexplainable halving of the number makes me question the accuracy of what's being reported.

I've gone through the calibration checks and everything that's meant to be toggled on is on. I also have Movement Calibration & Distance turned on and walk almost daily for >30 minutes, with Works Outs>Outdoor Walk on my watch recording each walk. Apparently this is meant to fine tune and constantly calibrate for accuracy.

Apple Watch 7 running WatchOS 10.4 (latest version at the time of writing).

Well I do not have an ultra or an ultra 2 as I’m stuck with a series 8 for the next few months but I can attest that I too have very inaccurate readings in regards to VO2 max specifically. I have lost over a hundred pounds and I see my peak heart rate during pretty tough and steep hill climbs over a 15km trail drop 20-30bpms over the last two years. All my other heart metrics are average or above average except my vo2 max which is consistently in the below average range now despite my overall fitness improving drastically. Another problem you may have is in apple’s infinite wisdom and even with their in ecosystem “health” integration they are unable to account for rucksack weight or weight vests. This may trick you watch into thinking based on your health data that your heart is unnecessarily under strain when there is actually a good reason —> dumbbells etc. How they have not addressed this yet is completely beyond me.

Actually, it hints at this right in the description in the health app

Hi nikolin51

did you ever get to the bottom of this? I’m experiencing the exact same issue as you. My cardio recovery has dropped to 24 from 45 as I progressively get fitter.

Its A bit worrying not knowing if it’s the watch being massively inaccurate or my heart response to exercise getting worse.

“The higher the better” part is disturbing but I’m thinking about your theory and hope you’re right. I researched reasons it might increase with better workout and some things that came up are dehydration, heart issues, and blood sugar issues.

Mine stopped recording fitness last June and the recovery been dropping sharply since September (40.1 to 15).

I unpaired watch from phone and now both don’t record any data 😂

don’t think that’s the case with garmin

Same. A few months late to the conversation, but googled same experience. Feeling better and fitter than long time. Now, Apple Watch alerted me tonight I am trending down. How? Why? Makes me want to stop wearing my watch. As my fitness declined over the last few years, I was showing as strong. Now that I am reclaiming it, I’m unhealthy?!

Perhaps you are on to something with the code improving. My oura ring is doing same thing….saying I am trending down, when actually my behavior (food, no alcohol, great sleep, exercise are all better than last couple years when it said I was “strong/excellent”). I’m about to throw them both out. 😂