I shouldn't bad mouth any kind of exercise, after all even if the only exercise you get is walking to your mailbox, that still is better than sitting on your butt watching tv ad nauseum. BUT, I have to weigh in on the great bike exercise treadmill vs debate. You see, I am a fervent proponent of exercise bikes simply because of one factor. I suffer from heel spurs. And let me tell you, if you've never suffered from these excruciatingly painful things, I probably cannot convey to you how much they hurt. Suffice it to say that the constant pounding of feet on a treadmill is virtually impossible with heel spurs. For this reason alone, I opt for an exercise bike which is painless on my feet.