I work really long hours, so i find that I'm faced with this decision quite often. I don't get enough sleep and I'm also trying to get in shape. But if i have 7 hours until i have to wake up, should i spend an hour working out even though it means I'm only going to get 5 hours sleep? (1 hour workout + 1 hour shower and relax time, since you can't fall asleep immediately after exercise) I know your muscles need proper rest or they don't grow, so the correct answer is to do both, exercise and get 8 hours sleep, but for those occasions where both is not possible, which one should i choose? And is the answer different for lifting than for cardio?