Last year about this time my buddy was all hardcore about getting a Road bike because his brother had just bought one and he'd taken it for a couple of spins and had got the itch. Then, a few months later, I bought a brand new MTB and he switched focus back to MTBing. However he's back on the Road kick and looking pretty regularly at new bikes. So the other day I was talking to our LBS guy and he told me that you should never switch between Road and Mountain biking or else you could cause physical damage to your body. Is this true?? Road biking a few days a week and then doing a MTB ride is going to screw you up due to different core muscle groups being utilized? I'm inclined to believe him because he is an absolute beast when it comes to biking. I know he told me he either does one or the other, since he does Road racing and Cyclecross.