My new (since 30th october) Forerunner 255 has very weird behaviour for V02max calculation. I started out from previous watch, a 645 with a VO2 max on 51 and with the new watch it has linearly sloped down for each day and training. Now it says 43 but continously dropping. With now correlation to what I experienc and real efforts. two weeks ago I set a PR on the half marathon and during that week VO2max dropped 3 points. Doesn't make sense.
Hi I asked the same some time ago..
There are many factors that come into play when calculating VO2 Max. Here are some examples of what may lower this number:
Here is some more information on the VO2 Max tracking: What Is VO2 Max Estimate and How Does It Work?
That is correct and the things you mention should probably affect V02 max. But I have not changed any of the patterns for my training and heart rate with the new watch seems to be measured even a bit lower, which makes the massive downturn even more strange. Of course there could be physilogical explanations, but I doubt it, since the steep downturn started exactly when I started to use the new watch.
Have you checked that all your stats (Max HR, age, weight, etc.) are correctly set in the new watch? They probably should copy over from the old one, but it's worth a look because that could explain the drop in VO2max.
Just my 2 cents, but I think max HR is the most important (and maybe only) physiological parameter that affects VO2 Max calculations for Garmin devices.
People always say that other stats such as age and weight need to be correct, but I've never bought that. Obviously age and weight affect your VO2 Max, but that doesn't mean they are used in the calculation for VO2 Max. My understanding of Garmin's VO2 Max calculation was always that it looks at your speed and HR data for a sub-maximal effort (throwing out data that isn't applicable, such as being stopped at red lights), and extrapolates to a maximal effort using your max HR. Then it uses a lookup table to determine your VO2 Max (maybe some variant of the Jack Daniels VDOT lookup table). This is based on the FirstBeat whitepaper for VO2 Max, which also says that other physiological parameters are *logged* (but says nothing about actually using them in the calculations).
(This isn't too dissimilar to those online VO2 Max / VDOT calculators which ask for a race result - time and distance - and spit out a VO2 Max based on that, except for the parts about throwing out inapplicable data and extrapolating from a submaximal effort to a maximal effort. Note that such "race result to VO2 Max / VDOT" calculators ask for no other information than race distance and time.)
In other words, if 2 people of different ages and weights have the exact same max HR, with the exact same pace and HR for the exact same distance, I would expect their calculated VO2 Max to be the same. I wouldn't expect age or weight to play any role in the calculation. Same goes for gender (another parameter that may *affect* VO2 Max in terms of population averages, but should seemingly play no role in Garmin's VO2 Max calculation).
As a concrete example, if 2 people of differing age, weight, height and gender happen to run a 10k race at max effort in the exact same time (e.g. 42:00), then I would say they have the same VO2 Max (or rather, the same VDOT / effective VO2 Max [*]). Similarly, if 2 people happen to have the same max HR and run 10k with the exact same HR for the same time, then I would expect Garmin to estimate the same max HR.
I could be wrong though. A FirstBeat employee (HermoT) once commented in these forums that physiological parameters such as weight are important to the algorithm, but I never really understood how.
I guess I could always tweak my weight significantly in Connect and see if my VO2 Max changes significantly (all other things being equal), but I've always been reluctant to do that test. Personally I don't think it should (if I actually lost a ton of weight, I should be able to run faster, all other things being equal, and therefore have a higher VO2 Max, but if I just *say* I lost a ton of weight without running any faster, why should my VO2 Max increase?)
I have gained about 5 lbs suddenly and recently (and Connect knows about it), but my VO2 Max has continued to increase steadily (as it has been doing for about 3 months). I realize that proves nothing ofc. However, the increase itself makes sense, as over that time, I've been running at same pace or faster but my average heart rate has been decreasing.
[*] VDOT is Jack Daniel's term for "VO2 Max" as determined/estimated by a race result. He uses this special terminology because it's not really your literal VO2 Max (which is a measurement of how much oxygen your body can use). In reality, 2 people who run a 10k race at the same speed can have differing VO2 Max values, with differing running economy closing the gap (for example). But with the Daniel's method of estimating VDOT from race results, 2 people who have the same race result will always have the same VDOT.
Similarly, "effective VO2 Max" is runalyze's term for the "VO2 Max" value that's estimated from speed and HR data (supposedly in much the same way that Garmin does it).
As far as I understand, VDOT is a basic indicator of run result as only consider distance and pace and you can get increased values only if you run faster, without attention to your heart rate. What worth this to? 2 people covering the same distance with same time but different HR, have same VDOT but different VO2max.
I am checking and record my VO2max after every runs, and I am stable at 46 while some weeks ago I was 44. The increase from 44 to 46 due to my HR max decreased, and my HR is sensibly decreased of ca. 7-8 units running at 5:40, imho.
First of all, that was more than 2 cents! :-)
But I think you are missing out on one important thing regarding weight. The unit for VO2Max is mL/kg/min. That means your VO2Max is inversely proportional to your body weight.
as far as I understand, VO2 max is highly depending on HR vs pace: if I run slowly with HR very limited (ca.120) VO2 max decreases, while I could attend to increase, but that's not.
I relized the fixing of the watch to the wrist, it must be perfect to evaluate correctly HR. In fact, I think my VO2 max was increasing from 45 to 47 due to wrong measurements (unfortunaletly!) as it measured less than the reality.
But I think you are missing out on one important thing regarding weight. The unit for VO2Max is mL/kg/min. That means your VO2Max is inversely proportional to your body weight.
I'm not missing out on that at all. Weight would indeed be very important if Garmin was directly *measuring* your VO2 Max / oxygen intake rate.
For example, if I did a lab VO2 Max test where I run on a treadmill with an oxygen mask strapped to my face, and the techs measure my oxygen intake, obviously weight will be used to calculate relative VO2 Max (in mL/kg/min as you said). [Ofc, there's also the concept of absolute VO2 Max in mL/min, but relative VO2 Max is much more useful and is usually what's meant by unqualified "VO2 Max"]
But Garmin is not measuring your VO2 Max at all, it's estimating it. My understanding is that Garmin apparently estimates relative VO2 Max by measuring pace and HR for a submaximal effort, extrapolating to a maximal effort (e.g. 10k race time). This is very similar (or even closely related to) the Jack Daniels method.
If I can run a 10K race at 45:00, this translates to the same VO2 Max by the Daniels method whether I'm 140 lbs, 250 lbs or 500 lbs. That's why the Daniels VO2 Max from race result calculator only asks for time and distance. All other factors (age, weight, height, sex, etc) are irrelevant, even though they can all play a role in how fast you run.
Similarly, runalyze has its own VO2 Max calculation which uses pace and HR data. My understanding is that it's very similar to what Garmin (I could be wrong), except without the Firstbeat "secret sauce" where certain data is discarded (like times when your waiting at a red light). Crucially, runalyze doesn't need your weight at all to calculate VO2 Max, and I don't think it uses your weight if available.
So I could be wrong, but I've thought about this a lot, and I still don't think that Garmin uses weight (directly) to estimate VO2 Max.
I could test my theory by making an outrageous weight change in Connect (like doubling my weight) and seeing if Garmin's VO2 Max changes wildly (maybe after a period of a few days or weeks), but so far I haven't like doing this haha.
VO2 max is highly depending on HR vs pace
I would say go further and say that Garmin's VO2 Max estimate revolves around the relationship between HR vs. pace, it's not just highly dependent.
It's all here in the firstbeat white paper:
https://assets.firstbeat.com/firstbeat/uploads/2017/06/white_paper_VO2max_30.6.2017.pdf
While the Garmin race predictor has evolved a lot over the years (it used to be a straight table lookup from estimated VO2 Max to race times, but now it takes mileage into account), I don't think Garmin's VO2 Max algorithm has fundamentally changed much. (For all I know the part where it discards bad data has been refined, but I don't think the essential foundation has changed.)
Sorry to make this a separate reply, but the forum won't let me add it to the other comment
That's why the Daniels VO2 Max from race result calculator only asks for time and distance.
ofc Daniels calls this "VDOT" to distinguish it from true VO2 Max (oxygen intake) which is measured in a lab. This is especially relevant since things other than your literal VO2 Max can effect race performance, like changes in running efficiency. Similarly, runalyze refers to "effective VO2 Max".
I will say that someone on the forums once claimed that Garmin actually estimates true VO2 Max and not VDOT. If that's the case, then there's def something big that I'm not understanding here.
