Interpret Health data properly: A lesson

Not long ago I had a bit of health scare, from which I learned a lesson in interpreting Apple Health data properly and getting proper medical advice.

Some time in May ‘22 I received a health trend notification that my VO2 max level had been decreasing while my average exercise heart rate had been increasing. I was a bit concerned since I thought I had not made much changes to my walking activities (more below).

In Jul 2022 I had been experiencing some palpitation and then some chest pain which got increasingly worse. I was then properly worried and went to my family doctor. He sent me to the emergency department of a hospital. I was given a panel of blood tests and ECG, but the results showed me to be in perfect health. The ED doctor played it safe and set up an appointment with a cardiologist.

The cardiologist was somewhat amused and assured me that all indications suggested that I was fine. He looked at my Apple Watch ECG readings and told me everything was normal. I asked about the trends, and he advised not to take them seriously except for the ECG readings. Looking at single measurements - even those taken in lab settings - did not mean much, and it was important to consider a whole host of factors before a diagnosis can be made. He asked me to watch out for the coffee I drink, that it was the most likely reason I felt the palpitations. (He was indeed correct.)

Later the “chest pain” resolved itself; I had long coding sessions and sat in various unhealthy postures, so the chest pain was not of the heart but the muscles!

A few days ago I figured out the reason my average heart rate had been increasing over the past few months. I thought I just walked at the same pace all these while, but I forgot that I changed my walking habits. I started to go back to office regularly and went for walks after work, carrying 20-25 lb on my back. When I was working from home, I walked without carrying anything and later in the evening when the weather was cooler. Of course my heart rate would increase! But Apple Watch did not measure all that.

I thought it will be good to share this to remind ourselves that ultimately, many of Apple Watch health measurements and metrics are just estimates, and these need to be considered in relation to other factors, such as lifestyle changes. It is also best to have regular conversations with the doctor to get proper medical advice.


There is some information in The Paramedic’s Guide to Blood Oxygen and the Apple Watch Series 6 - TidBITS

In medicine (I’m not a doctor but work as a medical statistician) often the only thing that matters is if a test is in the normal range or not. For oxygen saturation it is slightly more complex because there is a something is wrong range and also a range that is concerning.

Apple doesn’t tell users these thing probably because that would be a diagnosis and they don’t want to get into that area, and the FDA would need to approve it. They do flag abnormal ECG but don’t say what is actually wrong. Apple reduces their liability by telling people that they need to talk to their doctors to interpret any of the results.


Thanks for taking the time to post this, @chengengaun. It’s a reminder to be careful about interpreting any medical “symptom”, not just the electronic stuff! It’s great to hear that you turned out to be in good health after all.

I’m currently trying to get my head around the Walking Asymmetry data. I injured my ankle more than a year back and it’s taken a long while to recover. My iPhone occasionally claims I have asymmetry in the range 1–3%, and I’m wondering if is picking up an imbalance that I no longer notice myself.

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Hear, hear. IMO, Apple’s Health app, with all its related watch/phone inputs, is not a diagnostic tool. The data is simply the data. You should use that data as a springboard for discussions with your physician, not to magically elevate yourself to the level of expertise he or she spent years in school and experience attaining.

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