Vo2 max vs FTP

Hi, sorry to hear about the health ordeal, but relieved to hear about your recovery progress!

I'm certainly no expert, but here are my thoughts based on following similar topics for some time now.

I think the first caveat to keep in mind is that the metrics given by the FirstBeat algorithms from these Garmin devices are definitely no substitute for actual clinical tests (moreso in the case of VO2max). They are proprietary algorithms that rely significantly on empirical data -- meaning statistical data gathered from test groups -- and then attempt to map our own individual data into those stats. All largely based on HRV (heart rate variability) data. The level of "accuracy" of these predictions for any particular individual remains unknown (or at least not well-examined publicly).

Here are the VO2max vs age categories that Garmin uses: https://www8.garmin.com/manuals/webhelp/edge1030/EN-US/GUID-1FBCCD9E-19E1-4E4C-BD60-1793B5B97EB3.html

It seems that regular high-intensity activities are needed to form its best estimate of VO2max (and ideally with a power meter). If we're doing more lower intensity activities instead, the VO2max estimates can vary quite a bit (and I've seen reports of both unreasonably high and unreasonably low VO2max estimates as a result).

FTP is fortunately a bit easier to estimate, so I think the Garmin estimates have less variability than the VO2max estimates. We can also easily estimate ourselves with various FTP tests. Overall I would have much more confidence in FTP estimates than VO2max.

Of course FTP and VO2max are also not the same thing. Respiratory capability (such as VO2max) is only one component of what goes into our FTP capability, there is also cardiopulmonary, metabolism, muscular endurance, etc. Although activities that generally contribute to improvements in VO2max should also help improve FTP (and vice versa), there is more to the picture for FTP. And of course FTP is at intensities below VO2max.

With all that said, I would suggest taking the VO2max estimates with a grain of salt. If they're trending upward over time, it's probably a positive indication, and I wouldn't fuss too much over the age group comparison it spits out. Similarly for FTP, if it's improving over time, it's good news, and perhaps a "more reliable" indicator. Hope that helps, cheers!

...Just a follow-up to my ramble from last night to correct an error and add some clarity (I hope)...

Here is a Firstbeat white paper regarding their VO2max estimation algorithm: https://www.firstbeat.com/en/aerobic-fitness-level-vo%e2%82%82max-estimation-firstbeat-white-paper-2/ (and other papers on various Firstbeat topics are available here: https://www.firstbeat.com/en/science-and-physiology/white-papers-and-publications/).

Although they provide some general info about how they work, they are thin on details, tending to be vague and secretive. They read more like marketing materials than technical papers.

That said, above I suggested that it uses HRV for VO2max estimation, which appears to be incorrect according to that paper. Instead it's based on HR vs power data for cycling (or HR vs speed data for running). It still relies heavily on empirical/statistical trends.

In short, it appears to monitor your HR vs power data during activities to form a trendline (or curve), and then it extrapolates that trend to estimate your power at max HR (it therefore relies on a good estimate of your max HR). Then it estimates a VO2 for that power by using another statistical relation between cycling power and VO2. That VO2 is the VO2max estimate.

Some other demographic parameters may be applied as well, I think moreso when it's starting out and doesn't have much data to work with yet (the parameters include user profile info such as age, sex, height-weight, active time per week, etc).

The key points seem to be that it needs a good max HR estimate, and it regularly needs good data at higher aerobic intensities (so it doesn't need to extrapolate so far). This should result in more consistent VO2max estimates.

Many and sincere thanks Kyle, Sorry to have not responded earlier. I will certainly look into all the information you gave me. First I do have to digest your extensive info though. If there is anything that I do not grasp, and I am sure there is, I hope I can revert to you once more. Thanks again // Leif

Kyle J, To explain some more; I am 73 now and was diagnosed with malign pc ( gleason 4+5 if it is understandable ) and had it followed up by heavy radiation treatment 2 1/2 ago. Less than 10 years ago my Vo2 was around 46-47 (lab tests). I was not using wattpedals at that time so there are no watt inputs. Now after treatment my Vo2 has gone from 36 to 38 (Edge 1030), which is, ie still fairly ok for my age group. As I mentioned in my earlier posting, now using wattpedals, that what puzzles me is my watt per kg is 1,53 which is just about plain nothing and hitting even below the bottom of the scale. I find this strange and hence my post. I do feel I lost most of my power but still....that is extremely, extremely low.