Apple Watch vs Fitbit - providing me with very different fitness results

I’ve been wearing Fitbit fitness trackers from probably a decade now, and liked the lightweight models which were unobtrusive on my wrist and easy to keep on nearly all the time. The only problem I had with Fitbit bands was that, at least in the basic models I bought, they were hard if not impossible to read in bright daylight. So when my wife recently bought me the latest Apple Watch I was excited to have a variety of watch faces I could read. I also assumed the Apple would tell me I was just as fit as the Fitbit had for many years. No way.

Right from the start - and I’ve had the watch a fortnight or so now - it decided my fitness levels were substantially below Fitbit. Instead of being excellent for my age (63) I’d slipped to just above average. The two companies measure the fitness level with a number, representative of your so called VO2 max - the maximum amount of oxygen your body uses in hard exercise - and the higher the number the better. With Fitbit I ranged between 47 and 53 depending on how hard I’d been training. With Apple I am 34-35. Now, i think this is a pretty extraordinary difference and frankly I don’t pretend to know who is correct. I certainly don’t think of myself as a very fit person. I’m not a great runner, probably clocking around 28m for the 5km last time I ran it. I certainly haven’t taken a proper laboratory VO2 max test and according to those who have, it is pretty unpleasant.

But I have for a long time used an indoor rowing machine as a part of my fitness routine because it is demanding but not terribly long. The most I would row would be 5km and aim to break 20 minutes, but generally I’d go hard through just 2km and aim for something between 7m 30s and 7m 55s. Interestingly, the Concept 2 rower website estimates VO2 max from your times and between those I did for the 2km row, estimate a VO2 max of between 56 and 48. Yet the Apple Watch tells me my fitness level is, as I say, around 35. I have used its specific functions to measure rowing and the elliptical trainer, which I prefer to running, and clearly I’m just not cutting the mustard.

All this strikes me as a topic that it would be interesting for Choice to investigate. The key component of a Fitness tracker is to tell you how fit you are. Clearly, in my case, Fitbit and Apple cannot both be right. Yet they are making many millions of dollars worldwide from these devices. Maybe I am a rare case and most people get the same result, but that would seem odd to me given the correlation between Fitbit and the Concept 2 rower figures, but not Apple. The true VO2 max can be determined in a lab, so it would be possible to test the accuracy of the claims being made by these companies. I wonder if anyone has done this research?


I suspect both are ‘wrong’ to some extent.

Probably Apple and Fitbit use different technologies - or the same technology but different ways of assessing the raw data it provides. Apple’s methodology is described here, while Fitbit’s is outlined here.

These devices do not provide you with lab-quality or medical grade results; they are at best ‘a decent estimate’. (Apple has received certification for its ECG technology, but not for most of its other ‘wellness’ tech; similarly Fitbit has received certification for its own ECG tech.)

My overall suggestion would be that you stick with one brand. That way, you can see whether you are ‘improving’, ‘maintaining’, or ‘declining’ based upon however that brand measures your VO2 max. The movement is more important than the raw number.