Although if you can try to spend some time doing SOMETHING on your rest day. Maybe a little weight training (avoid your legs, and keep you HR down.) If I try to take a pure day off, I feel tired all day, and the next day I'm sluggish. Even a long walk will help (plus if you jog for a quarter of a mile or so the impact nature of the exercise will help your knees and bone mass as long as you don't over do it.)