The more cardio I do, the more my VO2 decreases

[Katalinax]

I have been working out since the start of 2017 but from late 2017 to the present day a lot more seriously. I used to be terrible at reaching my cardio heart rate, but more recently hit it for about 30-60 mins a day. (Average on most works out is 140-150bpm)

Recently, I have been focusing on increasing my VO2 and all it seems to be doing is decreasing. It doesn't at all match with my current fitness at all, which is quite good, but my VO2 stats do not read that. It increased to 34-39 which is better than what it used to be (I would like it in the 40-50s eventually), but still not where I wanted to be. Now, about a week later it had decreased to 33-37 which I really do not want at all. I do about 20mins running and 40-60mins med-high intensity on an exercise bike daily. I always hit 10,000 steps. My resting heart-rate ranges from 60-70, it acts a bit like a hill.

Does anybody know what the issue is? I am quite young if that would impact these stats at all. I do have quite a bit of muscle too, but am considered over-weight for my age. (Which isn't true at all.) Thanks 🙂

[WavyDavey]

Hi @Katalinax,

Welcome to the forums.

First, congrats on your work on cardio fitness. Getting into that zone for as much as you are is great for your health. It can be frustrating when that isn't reflected in the VO2Max.

Two things jumped out at me reading your post, that may be factors.

One is your resting heart rate, which has a wide swing to it, and is part of Fitbit's VO2Max calculation. I would have expected your heart rate to be no higher than low 60s. Not sure why it is, but that would definitely contribute to a fluctuating score. Has it always been "like a hill"?

Second, is muscle mass. My experience has been as I added muscle mass, the Fitbit system (like BMI and other measures) appeared to assumed that at a heavier weight, I must be less fit. This is independent of how much cardio I was doing. This is an issue that many weight lifters know of.

Here is an article from Fitbit on Cardio Fitness, which goes over how it's calculated, and has a section on improving your score. Hope this helps, keep up the good work.

[Alicat2104]

My VO2 gets up to 40-44 most of the month with RHR around 65-67 but drops to 39-43 for about a week before my period due to the slight increase in RHR that many women notice around that time. Could be what you're seeing?

I wouldn't worry about it, just keep doing what you are and be patient - these devices aren't medically accurate after all.

[Katalinax]

Thank you so much 🙂 and yes, it has always been like a hill. The average though every month looks to be about 65-67 bpm, though I do see it drop to as low as 59bpm during the day.

[Katalinax]

Thank you very much, it possibly could be yet I don't exactly know.