"Perhaps, some of us are over-doing it (including me, though to no ill effect so far). I'd be curious about other's reactions. (I got this from the Sound Cyclists group)
This is a provocative AP article stating that physically fit adults should do at least 30 minutes of moderate-intensity exercise like a brisk walk a day and physically fit people about an hour a day. The article then quotes Dr. Mehmet Oz a surgeon an author of ""You the Owner's Manual"", who states ""The real sweet spot, as you would expect there to be in any biologic system, is around an hour a day. ""After that it is hard to show a great benefit""
The important part of the article states it is difficult to say with precision when healthy exercise becomes unhealthy and quotes a Professor Haskell of Stanford School of Medicine and states the general risk of harm begins to outweigh the benefits for adults after more that an hour a day. Above an hour, its questionable whether you are going to get more from it, he said.
Dr. Oz says overexercise can create oxidative stress, in which oxygen molecules called free radicals are formed that damage DNA and cells that, over time, can accumulate to spur cancer. This is in addition to overuse injuries that often result from over training.
They state listen to your body and take days off.
Moral: everything in moderation.
Personally, I prefer to cross-train (hiking, mtn biking, skiing, running, hoops, etc.). I always kind of welcome the respite this time of year from road cycling.
http://hosted.ap.org/dynamic/stories/F/FITNESS_OVERTRAINING?SITE=AP&SECTION=HOME&TEMPLATE=DEFAULT&CTIME=2006-12-14-14-26-04"