VO2 Max calculation issue

To which version and when did you upgrade your firmware? what version did you have before? As there are issues with the OHR sensor data since f/w 17, that might also cause different VO2Max estimate.

Here is a possible explanation:

- you didn't run in April and May, so the watch started using your cycling VO2 Max as no running VO2 Max was available any longer for at least 30 days,

- your cycling VO2 Max is overestimated because the power data is wrong, your Max HR is wrong and/or the HR data collected during your indoor cycling is wrong.

That doesn't really explain why the running VO2 Max chart in Garmin Connect would start to follow the cycling VO2 Max chart. That part looks like a bug (or poor implementation decision) to me. Given that the watch keeps separate running and cycling VO2 Max estimates (regardless of which one is shown as the default VO2 Max on the watch), there doesn't seem to be a good reason for one estimate to take on the value of the other estimate.

To me it looks exactly like what the OP suggested: OP stopped running in April and May, so Garmin just used cycling VO2 Max in place of the missing running VO2 Max data.

FlowState said:

To me it looks exactly like what the OP suggested: OP stopped running in April and May, so Garmin just used cycling VO2 Max in place of the missing running VO2 Max data.

As I said earlier,

Etupes25 said:

- you didn't run in April and May, so the watch started using your cycling VO2 Max as no running VO2 Max was available any longer for at least 30 days,

FlowState said:

That doesn't really explain why the running VO2 Max chart in Garmin Connect would start to follow the cycling VO2 Max chart.

Yes, it does, except that I would have expected the green dot to be exactly on the blue dot at the change. Maybe there is some smoothing going on for the VO2 Max number at work to explain that.

Maybe I should have phrased it differently:

"yes it's a plausible explanation, but I think the behavior is incorrect."

As I said: "Given that the watch keeps separate running and cycling VO2 Max estimates (regardless of which one is shown as the default VO2 Max on the watch), there doesn't seem to be a good reason for one estimate to take on the value of the other estimate."

To be absolutely clear:

1) the fact that VO2 Max is displayed and kept separately for running and cycling implies that they are separate values, and suggests that it's incorrect for one value to automatically take on the value of the other. Otherwise, why keep 2 separate values?

Similar to max HR, VO2 Max is sport specific

https://nutrabio.com/blogs/endurelite/why-cycling-fitness-hardly-carries-over-to-running

KEY DIFFERENCE #2: VO2 MAX IS SPORT SPECIFIC

In an ideal world, VO2 Max would stay the same for cycling and running. Unfortunately, this is not the case.

By strict definition, VO2 Max (maximal oxygen uptake) is the greatest amount of oxygen that can be used at the cellular level for the entire body and is calculated using a number of variables such as weight and the amount of muscle mass utilized during an activity.

For the purposes of this article, running involves more moving muscles than cycling.

While both involve the lower limbs, running involves more upper body musculature recruitment due to arm locomotion while the upper body in cycling is generally stationary.

This is largely why VO2 Max will not be the same for cycling and running and why you might be gasping for air for the first few weeks of running.

2) Given 1), there's absolutely no good reason for the lack of running data to cause running VO2 Max to become the same as cycling VO2 Max in Garmin Connect. Again, I think this is incorrect behavior.

Etupes25 said:

I would have expected the green dot to be exactly on the blue dot at the change.

So in a hypothetical world where a person's cycling VO2 Max is 60 and their running VO2 Max is 30, you expect running VO2 Max to suddenly double due to lack of running data?

In OP's case, their running VO2 Max went from 52-54 to nearly 80 (same as their cycling VO2 Max), simply due to lack of running data and an increase in cycling VO2 Max.

Is there a reasonable physical interpretation for this? The only way it makes sense is if your running fitness necessarily follows your cycling fitness (but again why would running and cycling VO2 Max be calculated separately, in that case?)

Etupes25 said:

Maybe there is some smoothing going on for the VO2 Max number at work to explain that.

I think it's already pretty well-known that running VO2 Max is some sort of smoothed rolling average of per-activity VO2 Max, given its low variance (especially compared to runalyze per-activity VO2 Max, which is calculated in a similar way -- comparing HR to pace -- but can vary wildly from activity to activity).

If Garmin really has some algorithm which says "when running data is not available, just force running VO2 Max to be the same as cycling VO2 Max", it's not surprising that such a forced change would not be instantaneous.

But again, I disagree with that algorithm.

Just to be clear, the fact that the graph on Garmin connect will replace "VO2 Max" based on running with the cycling VO2 max is known behavior and explains what the user has seen. 

It happened to me when I got a broken foot in june that year, start indoor cycling in August, then picked up walking, later in August, then "running" later during the fall

It happened again a few months later in January after I pulled a muscle while running

FlowState said:

1) the fact that VO2 Max is displayed and kept separately for running and cycling implies that they are separate values, and suggests that it's incorrect for one value to automatically take on the value of the other. Otherwise, why keep 2 separate values?

This is not correct. One number is the overall best VO2 Max, the other one is the cycling VO2 Max. When no running VO2 max is availabe to impersonate the overall best VO2 max, the watch will use the cycling VO2 max. If the cycling VO2 max is not available, then the walking VO2 max, etc.

So the cycling VO2 max is not replacing the running VO2 max, it is just used as the estimate for VO2 Max when the running VO2 Max is not available.

Maybe it would be clearer if there was 3 lines or more: "overall VO2 max", "running VO2 Max", "Cycling VO2 Max", or "walking VO2 Max", but it is not the way it is implemented today.

FlowState said:

So in a hypothetical world where a person's cycling VO2 Max is 60 and their running VO2 Max is 30, you expect running VO2 Max to suddenly double due to lack of running data?

I would say their data is likely wrong. According to research, running VO2 Max is typically 10-15% higher than cycling. However this depends on the speciality of the athlete. A very well training biker can have a VO2 Max 5-15% higher than running.

But 100%, unlikely.

FlowState said:

In OP's case, their running VO2 Max went from 52-54 to nearly 80 (same as their cycling VO2 Max), simply due to lack of running data and an increase in cycling VO2 Max.

No, this is not what happened. See previous answers about what happens when no running VO2 Max is available. The running VO2 Max didn't increase, it stopped existing. What increased is the best estimated of VO2 max for the individual. 

First, it changed because running VO2 max was not available so cycling VO2 max was used

Second, for some reason, there is/was a big difference between the running Vo2 max and the cycling VO2 Max.

A difference is expected, based on research, around 10-15%, but in this case changing from 50 to 80 is unlikely.

So I conclude that one of the VO2 Max sources (running, or biking) is seriously off.

In my experience, after I have finally set my Max HR correctly, curated my data about Rest HR, pace, HR, etc., the difference between running VO2 max and cycling VO2 max reduced significantly, but my current VO2 Max for cycling is 2 points above my running one (which is not the typical case from research) but a very common occurence if you look at forums of Garmin users.

Garmin believes that their model is more accurate for running than for cycling (this is why running VO2 Max has the preference).

For the OP, a cycling VO2 max of 80 would rank him ~35 worldwide. So he is right to doubt his cycling VO2 max is correct.

https://www.topendsports.com/testing/records/vo2max.htm

For cycling, I am suspecting the error is coming from the power data. I found the cycling metrics to be highly depending on power, more than running metrics are depending on pace.

TL;DR I have a very hard time believing that:

- "VO2 Max" is either running VO2 Max or cycling VO2 Max, depending on the situation

- In the cases when "VO2 Max" refers to cycling VO2 Max, Garmin just won't show running VO2 Max

This is really absurd when you think about the implication that the VO2 Max graph (green line in OP's screenshot) is graphing 2 different things at different points in time, according to you.

Even if running VO2 Max is "only" typically 10-15% higher than cycling VO2 Max, it makes zero sense to collapse running and cycling VO2 Max into a single "dominant VO2 Max" for the purposes of a *graph*, especially when the dominant VO2 Max source (running or cycling) can hypothetically switch back and forth over time. (In the case of OP, it went from running to cycling, and when they start running again, it will switch back to running. What is the point of graphing the "dominant VO2 Max" if you have no idea *which* VO2 Max it refers to at any given point in time? I would argue that even showing a single data point for "dominant VO2 Max" is useless if you don't know whether it's for running or cycling.)

Etupes25 said:

FlowState said:

So in a hypothetical world where a person's cycling VO2 Max is 60 and their running VO2 Max is 30, you expect running VO2 Max to suddenly double due to lack of running data?

I would say their data is likely wrong. According to research, running VO2 Max is typically 10-15% higher than cycling. However this depends on the speciality of the athlete. A very well training biker can have a VO2 Max 5-15% higher than running.

Yeah, that was a bad hypothetical for sure.

I agree with what you said about how cycling VO2 Max must've been wildly overestimated in this case, but that's tangential to my main point.

Etupes25 said:

No, this is not what happened. See previous answers about what happens when no running VO2 Max is available. The running VO2 Max didn't increase, it stopped existing. What increased is the best estimated of VO2 max for the individual. 

First, it changed because running VO2 max was not available so cycling VO2 max was used

Second, for some reason, there is/was a big difference between the running Vo2 max and the cycling VO2 Max.

Etupes25 said:

This is not correct. One number is the overall best VO2 Max, the other one is the cycling VO2 Max. When no running VO2 max is availabe to impersonate the overall best VO2 max, the watch will use the cycling VO2 max. If the cycling VO2 max is not available, then the walking VO2 max, etc.

So the cycling VO2 max is not replacing the running VO2 max, it is just used as the estimate for VO2 Max when the running VO2 Max is not available.

Maybe it would be clearer if there was 3 lines or more: "overall VO2 max", "running VO2 Max", "Cycling VO2 Max", or "walking VO2 Max", but it is not the way it is implemented today.

This explanation is somewhat plausible (and consistent with what was observed), but reading between the lines of the help text, "VO2 Max" (without the "cycling" qualifier) is meant to be running VO2 Max.

Even if it was the way you say by design and implementation, I would argue it would be a very confusing and inconsistent design. For one thing, why did the "unqualified VO2 Max" (the green graph) not match cycling VO2 Max instantly, when running data was unavailable. Furthermore, if the best VO2 Max available is the cycling VO2 Max, then according to you, the running VO2 Max will be hidden (even if there's still enough data, just not enough to make it the "best" VO2 Max.) What if a user alternated several periods of not running and not cycling? This would make for a very confusing and uninformative VO2 Max graph.

And why would Garmin privilege cycling VO2 Max in this manner, especially given that their watches focus on running more than they do cycling (e.g. every Garmin watch supports basic running features, not all Garmin watches support power meters for cycling. There's a line of Garmin watches called "Forerunner", but no watch with a name that references cycling.) If it worked the way you said it did, cycling VO2 Max would always be available in the graph (regardless of whether it's the best source), but running VO2 Max would only be available if it's the best source.

This is the help text from the Connect website:

"VO₂ Max and Cycling VO₂ Max values may differ because the muscles used for each activity have different oxygen requirements."

To me this phrase implies that VO2 Max (unqualified) corresponds to its own activity (as Cycling VO2 Max corresponds to cycling), and the only activity that it can be is running.

The Connect app help text takes it further:

"Your dominant VO2 Max reading is used to determine Training Status. So if you've had more cycling activities than runs recently, Training Status will be calculated using cycling VO2 Max."

Notice:

- Again the implication that "VO2 Max" (without any qualifier) refers to running VO2 Max

- The help says that Training Status is determined by one of the two VO2 Max values. Notice there's no mention of a third VO2 Max value. There's no text that says anything like "the 'VO2 Max' value is your dominant VO2 Max, which is either running VO2 Max or cycling VO2 Max. If running VO2 Max is not dominant, then it will not be shown."

If VO2 Max / Cycling VO2 Max works the way you say it does, then Garmin:

- chose a very bad design

- has done a very poor (actually nonexistent) job of explaining it

Furthermore, certain Forerunners (such as 235) don't have the ability to calculate cycling VO2 Max. In these watches, there's just "VO2 Max", which is clearly running VO2 Max.

I think it's pretty obvious that for watches which do support cycling VO2 Max, Garmin simply added a new metric - "Cycling VO2 Max", without changing the name of the old metric ("VO2 Max", which was always understood to be running VO2 Max.)

If you have a source from Garmin that contradicts my understanding, I'd love to see it.

EDIT: yes I'm aware that Garmin will estimate unqualified "VO2 Max" from walking, if there isn't better data. Nowhere do they say that unqualified "VO2 Max" (*) can be estimated from cycling, though.

So if you prefer, I'll say that (unqualified) "VO2 Max" is for running/walking (but mostly running).

(*) (In the context of the metric that is also estimated primarily from running, and sometimes from walking.)

This is my third and last attempt to show you how this is working, as explained by the online documentation, and demonstrated by the behavior of the graph on Garmin Connect and the display of VO2 Max on the watch.

VO2 Max is an estimate that can come from different sources: running activities, trail or ultra running activities (supposedly only when the toggle is on in the settings), cycling activities, multisport activities,  walking activities or all-day heart rate.

What Is VO2 Max Estimate and How Does It Work? | Garmin Customer Support

Only when the watch is able to estimate your VO2 Max based on running activity, it will use that value for VO2 Max: training status and the green curve on the graph. If not, it will use the next best source if possible (there are four of them, plus the cycling VO2 Max)

FlowState said:

If you have a source from Garmin that contradicts my understanding, I'd love to see it.

Emphasis below added that shows that VO2 Max is not always running VO2 Max:

"Your overall VO2 max estimate is taken based on the following four activity types, listed in order of preference based on their accuracy."
The most accurate VO2 max estimate will display in Garmin Connect and will overwrite less accurate methods for 30 days. 

https://support.garmin.com/en-US/?faq=HVMcrDvQ3m2xEFh1aVMbU8

and about why and when cycling VO2 Max might be used:

"Your dominant VO2 Max reading is used to determine Training Status. So if you have have more cycling activities than run recently, Training Status will be calculated using cycling VO2 Max"

Connect help that you quoted earlier.

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I experienced what the OP is seeing on his graph, which is consistent with Garmin's documentation.

In the first graph I shared above, after getting out of the cast on my foot, my first VO2 max green dots in August and September 2020 were picking on the indoor biking VO2 Max source, despite a couple of qualifying walks. The watch continued using the cycling VO2 Max for the training status, and on the graph in Connect. Only in October, the green curve started following the new data from my new running activities.

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Now, I'd love to hear from the OP about his cycling VO2 Max.

Is there a possibility that the power meter is not correctly set up and is doubling the power unecessarily?