VO2 max dropping 15 points from one week to another

bmatos2 said:

I have set my max HR manually

There are 3 things for the user to do to get an accurate VO2 max estimate. There will still be a 5% error rate on average, so the error could be lower or higher, but 5% on average is very good.

a) Input and accurate Max HR value. An error of 8 bpm could triple the error rate in VO2 Max.

b) Use a chest strap during all activities to make sure the HR data is accurate. Even with a chest strap, there are risks with dryness/static electricity. Also, wear the watch during sleep to get an accurate average resting HR.

c) Keep a balanced training program, with a good mix of anaerobic, high aerobic and low aerobic efforts. From time to time, perform maximal efforts with 30s, 1mn, 4mn and 10mn interval repeats, or best effort races. This will expose the watch to a variety of HR/output combinations and improve the accuracy of the model

bmatos2 said:

and is the same for both sports

In practice, many athletes will be a higher Max HR and LTHR for running than for cycling than for swimming. Apparently, it can be explained away by differences in weight bearing and muscle mass involved.

That said, for the purpose of training metrics, there is, IMO, no need to worry about it. If you are worried about it, you would go do some lab testing and hire a coach to make the best use of the data in your training plan.

bmatos2 said:

my VO2 max - both in running and cycling - dropped 15 points from one week to another (48 to 33)

That is very weird. This is a huge drop within a week. It looks like a big change happened, like a change in HR Max, some really bad data from some activities, or an update in the model.

4684381 said:

Apparently runalyze can help here, viewing activity for the week showing VO2 max

Runalyze shows 2 types of VO2 Max:

- VO2 Max (by file): this is the *average* Garmin VO2 Max after each activity (same as what's shown on your Garmin, except Garmin rounds the value and runalyze shows 2 decimal places.)

- Effective VO2 Max: this is the per-activity VO2 Max that runalyze calculates based on HR and pace. It's similar, but not the same as Garmin VO2 Max.

You can tell the former is an average because it never changes by much (except apparently in this case), and latter isn't an average because it can vary wildly (especially if you run a race or you're fatigued/injured.)

The big gap here is you can never directly see the per-activity Garmin VO2 Max. You can only see how it moved the needle on the average VO2 Max. Since we don't know exactly how average VO2 Max is calculated -- it's clearly some kind of rolling average, but what's the time period and weighting? -- we don't have a way of calculating the per-activity Garmin VO2 Max either.

Another way to see the impact of an activity is to look at the performance condition of the run (i.e. starting and ending values.) Performance condition is defined as the % difference between your current performance (VO2 Max) and the performance predicted by your average VO2 Max. e.g. A performance condition of 5 means your activity VO2 Max (at that point in time) is roughly 5% better than your average VO2 Max. So if your performance condition was around +5 at least at the beginning of the run, there's a good chance your average VO2 Max went up afterwards. Similarly, a negative starting performance condition probably means your VO2 Max went down after the activity.

bmatos2 said:

Hi I've been running and my VO2 Max was ranging between 46-49 for several months. In Jan I went back cycling and my VO2 max - both in running and cycling - dropped 15 points from one week to another (48 to 33)

That's pretty crazy. As a runner, I've never seen that with current or older Garmins. Even after losing a ton of fitness during the pandemic by barely running, I never lost more than roughly 10 VO2 Max points in total, but that took over a year for me.

Clearly something is wrong here. Objectively you can't lose ~30% of your fitness in one week.

Maybe you should contact Garmin support ([email protected])

FlowState said:

Runalyze shows 2 types of VO2 Max:

This was in response to suggestions that the reason was "some really bad data on some activities". Of course, I meant VO2 max (by file), we were talking about its drop. In Runalyze, the dynamics can be traced in more detail, because the value is visible for each activity, and not only for those for which Garmin shows VO2 Max whether there is anomalous activity among all during the "fateful" week.

4684381 said:

This was in response to suggestions that the reason was "some really bad data on some activities". Of course, I meant VO2 max (by file), we were talking about its drop. In Runalyze, the dynamics can be traced in more detail, because the value is visible for each activity, and not only for those for which Garmin shows VO2 Max whether there is anomalous activity among all during the "fateful" week.

I agree, just wanted to clarify that, unfortunately, we can only ever see the average Garmin vo2max.