How useful are the fitness index, predicted max HR, vo2max features of the watch? Are they accurate?
Kim
I saw this lonely post, so figured I’d respond. I’ve been using my 710 since last sept. I have played with the features you list a couple times, just to see. web data suggests that they are reasonably accurate, though probably not accurate enough to really gauge your progress.
a friend and I both found that it predected the Max HR conservatively from data we’ve actually seen (I’ve seen 199 during an early season hard interval set, but I think my predicted was 192). our supposition was that they were going a bit low to avoid and legal problems of people hurting themselves trying to get to 95%, or something.
I’ve done the vo2max thing a couple times and gotten similar results each time, so the variance didn’t seem to bad.
I’m not sure how useful these features are. I gauge my fitness more from benchmark workouts, or group training. otherwise, we ought to just show up to races and compare vo2max’s. 
all that said, I love my 710 and the only way you’d get me to part with it is with a nice 720. but that’s based on the ExeSet and altimeter features. and getting rid or my other bike computer. what’s that quote about perfection not coming from adding things but from taking them away. I feel my bike is more perfect by having less stuff on it. but that’s just me.
thanks for the reply! do you know how they do the estimates, though? any websites i can check out?
Kim
I believe I’ve seen the formulas that polar uses on the polar support site. navigation through their web is horrible, I often can’t find things twice. I have had pretty good support through their email alias, so you could try that too.
somewhere on this board is a link to an australian chat board that discusses all kinds of polar related topics. I remember the work performance is in the link and it’s in the .au domain.