I'm tall and thin (6'2, approx. 160-165 pounds), and have always been in reasonably good shape. Since I've picked up biking I've noticed a definite improvement in my legs (obviously), my ability to sustain long periods of cardio strain (obviously), but also (not so obviously!) I have noticed more definition in my arms. I seem to have peaked now, so I'm in the process of looking for a free weight kit to balance out my routine.