When I've been concentrating on one leg, primarily on the left, my weaker leg, I just relax the right and let the left leg do most of the work. I may be doing it wrong--I'm a bike trainer noob. The trainer may become a more integral workout, but at the moment, I have it so I can still ride on days that are unridable or if I don't have the time to do an outside ride. I have to keep up the time on the bike since I have my first centuries coming last part of April and the first part of May.