When should I exercise? The best answer is: whenever you are most likely to do it. But there’s some science behind when to exercise to get specific benefits. Daniel Pink’s new book: When: The Scientific Secrets of Perfect Timing, explains.
Exercise in the morning if you want to:
Lose weight: You can burn 20 percent more fat if you exercise first thing in the morning, before you eat breakfast. (Journal of Physiology, 2010)
Boost mood: Cardio workouts make you feel good by raising endorphins. Do it in the morning and you get a lift that lasts all day long. Serotonin is another feel good hormone that peaks during the day and is elevated by aerobic exercise. Because these hormones peak during the day, if you exercise in the evening and raise those hormone levels, you risk difficulty sleeping.
Build Strength: Testosterone is elevated in the morning – yes, even for you, ladies. Testosterone helps build muscle. Take advantage of higher testosterone to get the most out of your strength-training program by pumping iron in the morning.

Be consistent: Many people say that no matter how good their intentions are, if exercise doesn’t happen first thing in the morning, it won’t happen. So if you struggle to be consistent with exercise, do it before you can come up with an excuse. Studies have shown that people who exercise in the morning have a slightly easier time being consistent about it.
Exercise near the end of the day if you want to:
Avoid injury: Body temperature peaks in the later afternoon and early evening. A higher internal temperature keeps muscles warm, more flexible, and less prone to injury. Studies have shown that injuries are less common during late day workouts.
Perform Best: Lung function is best later in the day. It’s no accident that the professional runners start last in the Bolder Boulder and a disproportionate number of Olympic records are set in the late afternoon or early evening. Your reaction time and hand-eye coordination are at their best later in the day as well. That might be the best time to schedule a tennis lesson, learn how to high jump, or other high skill activities.
Enjoy Your Workout: When exercise happens later in the day, people typically report a lower level of perceived exertion, even when they are doing the exact same workout as they did in the morning. Exercise can be more enjoyable when you wrap up your day with a work out.
You Decide!
So whether you’re a morning person or a night owl, think about what you want from your exercise, and time it accordingly. And, if any aches or pains create a further impediment to moving, we are here to help. Remember, there is no pill that can replace the medicinal benefit of movement.