A better question would be "how many days per week is too much?". If you're out of shape, 5 days per week isn't going to do you any good and may even be counter-productive. If you still feel tired after a good night's sleep, you are training too much and need to cut back until you're in better shape. This goes for every sport ever. If you over train, your body shuts down in an attempt to keep you from hurting yourself. You need to give your muscles time to recuperate and heal. If you insist on training 5 days a week, I would say it's better to train monday, tuesday, wednesday, skip thursday, friday, saturday, skip sunday.