Between cycling and running I don't do legs. Upper body always a problem (or should I say motivation) for me. I'll do upper body (ideally) on off days (2-3x per week) just to keep some tone up there. Of course my goal is to just stay in shape. Size does not really matter at this point. If you are building, you may be lifting too often. If you are just trying to get a work out or stay in shape, keep it up as long as you are not in pain everyday.