I am not “fit” but I do work out regularly. My VO2 max has dropped significantly since I had an ablation for AFib, which is so wild to me bc after the initial recovery I have been working out for months again now and I thought doing really well. So technically just looking at the numbers mine was above average before the procedure when my heart was all over the place and I routinely had to stop due to shortness of breath, but now it’s low even though I maintain a nice elevated heart rate during exercise and bounce back well, no shortness of breath. All that to say I love my watch but agree the algorithm must not be the most reliable in this aspect.