Originally Posted by
lil brown bat
Well, no, they don't -- but if you understand how scientific research happens, you also understand that simple and comprehensive answers like the one you want are not arrived at by a single study (if, indeed, there are any simple answers at all). Expecting such answers is unreasonable.
It's more of a wish than an expectation.
Anyway, another thing that is interesting to me is how much the human body differs from our mechanical creations. By stressing the mechanical device, we speed it's demise. By stressing our bodies (in moderation), we make them stronger. You would think that limiting the impacts and loads on our bones during exercise would help keep them healthy, but it turns out that that is not necessarily true.