Originally Posted by eandmwilson

Back to the original question, your legs won't likely get any bigger, though they may change shape from toning. For resistance training to really result in muscle growth, you have to routinely push through the anaerobic threshold, which is next to impossible to do while commuting simply because if you did, you'd very shortly fall off your bike as your leg muscles starved. What you are encountering is harder aerobic work, not what most people whom train with weights for bulk would call "weightlifting". Yes, you will get in better shape, and yes, you will get stronger, yes, your legs will tone but don't expect Lou Ferrigno thighs from a bike or any aerobic exercise!