That's true, but you missed my point. If the left leg is passively resting on the pedal, not actively pushing down. then the work of lifting it can be done by the right leg pushing the right pedal, and it's no more difficult than pulling up. It's the same as the way it takes the same effort to lift something whether you pick it up with your hands, or hoist it with a rope and pulley. And as alanbikehouston pointed out, pros don't pull up, at least on the trainer in the lab.