Sharp drop in VO2 max overnight, from a steady >37 for months ending on Dec. 31, 2025, to 33 on Jan. 1, 2026. This is the second time there’s been a sudden, inexplicable overnight drop in VO2 max on my Apple Watch. I now think these numbers are completely fabricated. Why does this happen? How can we trust this metric when it changes dramatically overnight for no reason?
I have seen cardio fitness drop like this some time ago end of year, though it has not happened to me.
All these estimated metrics are there to show a trend. Start from here and watch it grow or reduce over the year.
The only reliable VO2 measurement is in a medical lab with a full face mask on a spin bike and a $100K analyser. It would be very different if other reports are to be believed.
Its why stick to an SE watch because talk of hypertension, glucose and similar "indicators" fills me with horror.
38 to 33 overnight from 12/31/25 to 1/1/26, no change in exercise rate. If anything, I’m exercising more in January than in December, but my VO2 max remains steadily in the 33 range. Whatever is going on, it doesn’t reflect my fitness level. It’s ridiculous. This happened a few years ago, when a previous Apple watch dropped overnight from 42 to 38 after a software update. Totally unreliable metric.
How big a drop?
Another sharp drop in Apple Watch VO2 max overnight
