According to research on circadian rhythms, body temperature, and muscle strength, it's best to workout in the late afternoon.
Your brain follows a delicate schedule known as circadian rhythm. It's like an internal clock, and it controls your body temperature. By the afternoon, your body temperature is 2 degrees warmer than in the morning. And because of that, your muscles are more supple and warmed up, so you're decreasing your chance of pulling a muscle or getting injured.
Exercising in the late afternoon gives your body a chance to wake up, and you'll have already eaten 2 meals, so you'll be fueled up and have more energy.
Another thing, if you exercise in the late afternoon or early evening, you'll have a chance to get your work done. Your mind will feel more settled and calm, and your afternoon workout will be something to look forward to, a way to release.
But some experts say that working out in the morning jump-starts your metabolism. They say that morning exercise promotes more fat burning, but the difference is so small, it doesn't really matter.
Exercising before you start your day might be the only time you can be sure to fit it in, because once your day starts going, it's hard to break away from work and family commitments.
Fit's Tips: The bottom line is - you've got to find a way to realistically work exercise into your life. It has got to be compatible with your personality and your schedule. Whether it's at 5am or 5pm, set aside at least 3 times during the week that you can exercise.