I read the white paper on Firstbeat's site (Garmin licenses the software from Firstbeat) but there's nothing relevant in there.

I'm pretty sure my FTP has gone up enough that I need to test it. I got an IF of 1.164 last night doing hill repeats, it was tough but not "one for the books." There are other things that tell me I'm getting stronger, like RPE, and the fact that I'm using smaller cogs compared to a few months ago.

My weight hasn't changed much in months. HR is harder to get a handle on but the max HR I achieve in each ride has gone down slightly over the past year.

My Garmin says my cycling VO2max has been going down, at the same time it says my running VO2max has been generally rising.

I thought it was measuring HR/watts as a function of body weight, so if my power is going up and my weight hasn't changed, I don't understand what's going on.

I have no idea how it does it (algorithms?) but I am kind of curious as to what numbers it's spitting out for other people. For whatever it's worth, my 520 is giving me a VO2 max of 53.

Wait. How do I get VO2max on my 510?

I wouldn't worry about V02 max. It's basically good for bragging rights. You don't train off it. You've got power data, and that's what you need to train.

Also a calculated V02max is likely not to be terribly accurate.

Back in the day, when I didn't have a power meter, and had a sponsor that paid for lab testing I got V02max done in a lab. Never used the data for anything. Ever since I got a power meter, I haven't bothered with lab testing. It would seem to me, a calculated approximation for V02 max would be even less useful.

^this. The only real way to know is with a lab test. It's nice to know but that's about it.

I'm finding the long term (6-12 month) trend kind of useful, it helps me see whether what I'm doing is working or not. I can understand how only ever having had one test wouldn't be good for much but I basically have one done every time I ride or run, and I've seen a 3 point drop since May 9 for cycling.

How do you get the v02max from the 520?

My garmin profile has one I added that I calculated from my FTP, but I can't find the equation in my bookmarks.

The much more useful number to track is FTP

It does the computation automatically whenever you ride at/near threshold for a certain amount of time. When the ride gets finalized, it will pop up the VO2 max number on a little colored wheel. If you're not looking at the screen after you hit save, you'll probably miss it. I thought it would be stored in the Connect App under performance, but mine just says "No data" for both VO2 and FTP. Perhaps I don't have enough data recorded (only 10 rides since I got the 520) for it to update in the app? Dunno. Time will tell.

You don't think you can only track one or the other do you?

Try https://connect.garmin.com/modern/re.../all/last_year

I must need to update my 520 software again.

No. My point is FTP is actually useful in a training program ( and is more trainable than VO2 max) VO2 max, particularly when it's an estimate derived from FTP just isn't that useful.

I don't see the point worrying about VO2 derived from power data. At best it's one step removed.

Arise from the dead, thread!

I was searching for info about how Garmin estimates VO2Max and came upon this thread. But anyways, it appears that there is indeed a correlation between HR and power, and that it is quite easy to fool the system too:

I noticed when I do intervals above threshold at high cadence (e.g. 90-100rpm), my HR tends to be higher and at the end of the workout, my Garmin reports my VO2 Max going down. On the other hand, when I do the same type of over-threshold intervals but at lower cadence (e.g. 60-80rpm), my HR tends to be lower and at the end of the workout, the Garmin says my VO2 Max has gone up. It's very easy to "game the system" this way, last night I got my VO2Max back up from 58 to 60 just by doing low cadence work for the past two days so... yeah, it's totally an unreliable metric like others have mentioned.

You need a powermeter and a chest heart rate monitor (capable of HRV readings) or a footpod and a heartrate monitor (for running), then after a month or so of collecting data it will give you independent numbers for cycling and running.

I'm 25 years old, 5'7" 135lbs.

For cycling mine currently shows 68 VO2max, I use a Garmin 820 Edge, a Wahoo Tickr X, and a PowerTap G3 power meter. I weigh 135lbs and have a 290 FTP.

For running (which I just started getting into...) it shows 55 VO2max, I use a Garmin Forerunner 735xt, a Wahoo Tickr X, and a Garmin Footpod (calibrated using GPS runs outside). I can run a mile in around 6:30 minutes/seconds.

Throughout the season the cycling number varies, going as low as 62 VO2 max during high humidity 90+ degree weather (makes HRV dip and % maximum HR go up for a given sub-maximal exercise, because that's how heat affects ya) and as high as 74 VO2 max during winter (when training inside at 60 degree temp with low humidity, perfect conditions). I'd be interested to see of the Garmin 530/830/1039 and their "temperature acclimation" update would cause this variance to change...

It's not derived from FTP, it's derived from Heart Rate Variability and % of maximum HR at submaximal steady-state exercise sampled at the beginning of a workout. If you use the data field "performance condition" it will show you + or - your current status and your most recent HRV, you can use this figure on long rides, e.g. if it's plus 5 near the end, go hard, if it's -10 at the start, take it easy. It's similar to looking at what your HR is for a given power output sampled throughout the ride, but more accurate and sampled at periods that seem to try and eliminate artifacts and things like cardiac drift.

If anyone finds this thread and is interested in knowing more, here is the paper that describes the way Garmin estimates VO2 max from heart rate and power data:

Automated Fitness level (VO2max) Estimation with Heart Rate and Speed Data

I'm 64

Garmin thought my VO2max was 73 last Fall. Thankfully, they downvoted me to 71 today. I suspect even Greg Lemond would not carry such a VO2 Max when he reaches 64. What a joke algorithm.

Is your HRmax set correctly? Garmin defaults to the standard 220 minus age estimate, or 156 for a 64-year-old male.

The white paper states that if your estimated HRmax is 15 beats too low, the error is 9%.
If your HRmax is 15 beats too high, the error is 7%.
If your HRmax is exact, the error is 5%.

VO2max is interesting as a measure of cardiorespiratory fitness (stroke volume, gas exchange, blood O2 carrying capacity, etc), but I don't know how they can factor out muscular efficiency. They don't know your blood volume or lung volume, to begin with. If I were to guess they look at energy over some time window at LT and derive metabolic threshold energy, and from that infer how much O2 is consumed at LT. I doubt that's better than a rough fitness estimate. For training it's not very useful (other than you want to keep your cardiorespiratory fitness pegged, or training will suffer - but that's easy, and beyond that... meh).

VO2Max measurement pre-dates power meters, and is a summary measure of overall aerobic production of energy that could be measured without getting into the weeds of exactly how that energy was produced. What Firstbeat (and others) are trying to do is to find a way to approximate VO2Max from power data