you're only done when somebody throws you into a 6 foot deep hole and starts shoveling dirt on you. There's a guy at my gym who is 58 yrs old and lost both legs in Vietnam. He does an hour of cardio on the treadmill or elliptical machine with artificial legs. Then he lifts for about 45 minutes. He's a good inspiration when I think I'm to old and/or tired to do my boxing workout.