The Best Time to Work Out

Is it better to exercise in the morning, or later in the day? Let your circadian rhythms be your guide.

In the afternoon or early evening, your core temperature is warmer. A warm core makes your muscles and joints more supple, which helps you avoid strains and sprains. That makes afternoon or early evening ideal for exercises that tap your muscles, like strength training, stretching, and interval workouts.

Mornings Are for Endurance
On the other hand, if endurance activities are more your speed -- long brisk walks or bike rides -- morning may be better. Your body’s core is cooler early in the day, which can make endurance activities seem less tiring. And there is less risk of overheating. But a good warm-up will be key, since your muscles are likely to be stiffer in the a.m.

http://www.realage.com/ct/shape-up-slim-down/workouts/tip/7943