You may have heard it's best to work out in the morning because you might get busy in the evening or blow it off after work, and some say it gives them an early energy boost.
But if we're talking peak performance, you may be better off exercising in the late afternoon.
A study in The Journal of Strength and Conditioning Research shows that's when strength and flexibility are greatest. And perceived exertion, how hard it feels like your body is working, is lowest.
Scientists say that's because our circadian rhythm causes body temperature to rise throughout the day and peak in late afternoon.
What about burning more fat?
Some swear by what's called fasted cardio: working out in the morning before eating anything.
But two studies have shown fat loss is about the same whether or not you have breakfast before you exercise.
Overall, the best time to exercise is when you'll actually do it.