When I was in high school I worked out in the middle of the day after school. When I was in undergrad I would work out in the middle of the day or sometimes late at night anywhere from 9pm-12am depending on whether i was bored or wanted to procrastinate studying. After graduating, I mostly worked out in the evening after dinner because I am not a morning person. No way I could wake up with enough time to drive to the gym, drive back and get ready. I'm not yet in the stage where I'm willing to walk around a locker room naked like all the other old guys at the various 24 Hour Fitness gyms I go to. Maybe when I'm 50. Now I'm in law school, I 've been working out in the mornings since I don't have class till the evenings. I find that my cardio is much more effective on an empty stomach, and with a better diet, have seen real improvements and have gotten pretty lean. It's almost as if all the time I spent working out at night during my working days was useless. Hardly any changes to my body. Morning workouts force me to get up (but not as early as I would have if I actually had a real job), give me a good start to my day, I feel good that I've gotten working out out of the way, and working out in the morning makes me want to eat healthy throughout the day. If I stop working out or do it at night on rare occasions, my diet gets out of whack.