VO2 max, the amount of oxygen the body can utilise in 1 minute is widely recognised as the most important factor in endurance sports performance. Garmin’s VO2 max feature however, could be misleading you significantly.

 

Whilst VO2 max is a very important factor to consider, don’t overlook lactate threshold and lactate turnpoint. Marathon running studies and the first “Breaking 2” attempt have found that the highest VO2 max doesn’t necessarily predict the fastest runners, since other factors such as lactate threshold and turn point have an impact also. Essentially one person could have a higher VO2 max, but if they can only maintain the speed relative to 70% of that value for the marathon distance, they’d be beaten by someone with a slightly lower VO2 max if that person can run at 75% of that value for a marathon.

 

Garmin are guessing VO2 max

When Garmin assesses your VO2 max, they’re making a fairly big assumption. They essentially use your age to say where your heart rate should be at certain speeds if your VO2 max was X, Y or Z. I’ve addressed this age related max heart rate issue in another blog as well. Whilst there may be some correlations, the people who come up with the equations for Garmin have admitted that they can be up to 9% inaccurate, but usually fall with a 5% accuracy range. 

5% might not sound like a lot, but for a 9-minute mile runner for a marathon, it could be predicting you an unrealistic 27 seconds per mile faster or slower, equivalent to nearly 12 minutes. 

I had my VO2 max lab tested in 2017 when I was running around 25 miles per week and running 38 minutes for 10k and around 85 minutes for half marathon. It gave me a reading of 64ml/kg/min. In 2020 running far more miles, and faster times (35 minute 10k and 77 minute half marathon), Garmin says my VO2 max is 60ml/kg/min. There’s no way this has dropped, and 4ml/kg/min is quite a big difference.

 

It doesn’t take into account recent performances

Back when I used to take a look at the race predictor every now and then, I came back from running a 35:44 10k, what was my PB at the time, and it suggested I could run 36:32… even though I’d just run the distance 48 seconds faster. It also suggested a marathon around 3:05:00, which I knew wasn’t right as I’d run 2:51:43 a few months before with a 10k PB just under 37 minutes.

Aside from VO2 max, running performance over 10k to half marathon is one of the best predictors of marathon performance for trained marathon runners.

 

There’s no disclaimer

Now hopefully anyone reading this doesn’t need to be told that race predictors have the caveat that you’re trained specifically for that distance, but Garmin’s race predictor doesn’t seem to specify that anywhere. Not on the watch widget, and not on Garmin Connect, so unless you’re someone with a decent level of understanding and/or experience, you could very easily be led down the wrong path and set yourself up to fail.

 

I love Garmin products, they’re easy to use and the app is fantastic. My only gripe is that they seem to want to add features that don’t really add any value, and if anything could be doing more harm than good.

 

With their VO2 max feature, not only are they ignoring significant metrics (some of which could be used accurately), they’re making some big assumptions about the one metric they do use and leaving you none the wiser. 

 

Written by Kyle Brooks, Running Coach based in Norwich, Norfolk