My knees hurt too you make a good point. Needing some perhaps recuperative time for joints to rest as we get older seems more and more important to me.
Map Man- What would be interesting also (and maybe you did already and I just missed it) is if the study showed the ages of those that laid up longer to differentiate...I'd be curious anyway.
Mykneeshurt-I love my ipod too, neat little invention indeed, and the memo feature I use everyday.