The FitBit vo2max estimate is fairly crude, at least for my model. It requires a ten minute run on level ground at a certain heart rate to "calibrate" but trie

The FitBit vo2max estimate is fairly crude, at least for my model. It requires a ten minute run on level ground at a certain heart rate to "calibrate" but tries to estimate it from other exercise too. It leads to the number fluctuating quite a bit between runs and other exercises. I'd argue that how you feel during a run or hard cardio training is a better metric. You can fairly easily judge progress week to week, completely subjectively.