It depends on the MTB'ing. If you're riding smooth XC trails, your bikes should be set up about the same (maybe a little more upright on the MTB, but not a whole lot different than riding on the tops of the road bike), and the muscle groups are the same.

If you're hitting roots and stuff, that uses different muscles to control the bike, and also probably a higher gear (lower cadence) to be able to ratchet and power through tall stuff.

If you're dirt jumping or riding a pump track, those are much different muscles (believe me, pump track will work muscles you didn't know you even had).


It sounds to me like the road bike doesn't fit you very well. It might fit you now, but you already rode it a long way (for you) before you got fit. That's likely what is causing your pain.

Did they raise your seat during the fitting? Patella pain is from having the saddle too low, generally.