Forerunner 255 VO2 max? what's wrong?

I will also say that obviously if your weight changes irl and all other things are equal, your VO2 Max (both real and Garmin-estimated) will likely change. But I think Garmin's method will automatically account for this due to the fact that your running speed will also change.

It's the same reason that the Daniels VDOT calc doesn't need your weight even though it estimates VDOT / effective VO2 Max, whose units are still mL/kg/min.

I will also point out that mL (of oxygen) are in the VO2 Max units (and definition), yet Garmin (and the Daniels calculator) don't measure mL of oxygen at all or ask you to provide any data related to oxygen.

So that means our running speed is also inversely proportional to our weight, then. Maybe close enough for estimation purposes? 

ovekvam said:

So that means our running speed is also inversely proportional to our weight, then. Maybe close enough for estimation purposes? 

Right but my point is I don't think Garmin directly uses weight as a factor in estimating VO2 Max. That's why I don't think your weight needs to be correct in Connect for VO2 Max estimates to be "accurate".

Losing a bit of weight should make you run faster (as long as it's fat and not muscle, and all other things being equal), but I don't think Garmin needs to know that you lost weight to calculate a higher VO2 Max value. Similarly, if I actually lose weight but somehow I manage to run at the exact same paces for the exact same heart rates, I don't think my VO2 Max value will budge at all.

I could be wrong but I explained my reasoning in great detail. Notably, runalyze and the Daniels method for estimating effective VO2 Max / VDOT don't need to know your weight, either.

And again if anyone wants to try doubling or halving their weight in Connect, they could prove me wrong. I guess nobody has ever done that for the same reason I don't want to do it - bc I don't want to mess up my Garmin data just to prove a point.

By the same argument, I don't think Garmin uses age, height, gender, body fat %, etc. to estimate VO2 Max, even though those are all things that affect your running speed.

I've heard that argument that weight must be taken into account because it's in the units of VO2 Max many times, but it's funny that the same people who say that don't consider that mL of oxygen is also in the units of VO2 Max, yet Garmin doesn't actually measure oxygen intake.

Sorry the link you posted doesn't work... It would be appreciated if we can take a look on it.

Thanks

My b, I fixed it in the original comment and here it is as well:

https://assets.firstbeat.com/firstbeat/uploads/2017/06/white_paper_VO2max_30.6.2017.pdf 

I will also say that the one physiological parameter which is def used by the Garmin VO2 Max estimation algorithm is max heart rate (that's how the algo extrapolates a maximal effort from a submaximal effort).

Thank you for the link. BTW, I can say that my HR max was 162 till one month ago, then Garmin automatically changed to 164 and in the meantime my VO2 max decreased. So that's what I saw and support your statement.

5858725 said:

Thank you for the link.

You're welcome!

5858725 said:

BTW, I can say that my HR max was 162 till one month ago, then Garmin automatically changed to 164 and in the meantime my VO2 max decreased. So that's what I saw and support your statement.

Actually, I would say that an increase in HR max should lead to a higher VO2 max estimate (all other things being equal). And a decrease in HR max should lead to a lower VO2 max estimate. 

The reason is because if your HR max is higher, then for any given effort with a heart rate lower than the max, the maximal effort should be faster. (This assumes a linear relationship between pace and HR as per the firstbeat white paper that was linked).

e.g.

Bob runs 10k in 50:00, with a heart rate of 150. His max HR is 180.

Alice runs 10k in 50:00, with a heart rate of 150. Her max HR is 192.

Alice's extrapolated maximal effort should be faster than Bob's, since her 10k effort at 150 bpm represents a lower proportion of her theoretical max effort, compared to Bob's effort, due to the fact that she should be able to push her heart rate higher than Bob during a max effort.

It's the same idea behind hr zones which are expressed as % of max HR.

If your VO2 Max decreased, I can only guess it's because you *also* ran slower for the same heart rate as before (or the same speed for higher heart rates). 

If you did not run during the period that your VO2 Max changed, the change could also be attributed to older runs no longer being considered for your current VO2 Max. (Garmin VO2 Max appears to be a kind of rolling average which takes into account activities from a certain window.)

Here below my last 9 workouts:

If you look at the last workout, my pace was faster than the others (5:33), consequently HR max was higher too. My VO2 max was decreasing from 46 to 45, and in my understanding my heart was obliged to higher bpm in order to counterbalance the less capacity to carry oxygen. Probably I misunderstood something but what I can see is if HR max increases, VO2 max decreases!

Let me say that probably there are errors in the HR measurements, as I discovered HR increase just if my watch was more tight to the wrist. For this reason, I asked if it was possible that a loosen watch could affect HR measure and I got a detailed answer (probably not linked to the watch loosen or tight) but unfortunately I did not fully understand. Here below the snapshot of the answer where the graph is exactly what happened to me. There is a sudden increase that was (in my case) at the same time I tightened more the watch.

The page is a Garmin official page just typing "Garmin Watch Optical Heart Rate accuracy tips"

Could you comment the explanantion in the snapshot? 

Thanks!