Related Media: Overcoming Your Obstacles to Exercising

Exercise physiologists have found some differences between athletic performance in the morning and later in the day. Many of these differences are attributed to the body’s circadian rhythms—24-hour cycles that control physical and behavioral factors such as sleep, mood, metabolism, and body temperature. These cycles are driven by signals from the brain and other organs in the body.

Improving Fitness and Mood

If you are looking to improve your fitness, lose weight, enhance your mood, and/or just have fun, the best time to exercise is the time that you will consistently do it. The differences measured in research labs will likely have little bearing on your enjoyment and fitness level. In fact, researchers who looked at decreased anxiety and improved mood found that exercise at any time of day was equally as effective.

Shaving Seconds

For more competitive athletes, the time of day you do your most vigorous workouts does appear to have an effect. Researchers believe that workouts are most productive when body temperature is at its highest in the late afternoon. Body temperature is at its lowest 1-3 hours before waking up in the morning, and gradually increases throughout the day. This increase is small—only about 1-2 degrees—but appears to be enough to boost muscle flexibility and strength.

Studies have shown that exercising in the late afternoon results in better performance and more power. Because your muscles are warm and more flexible, your perceived exertion is low, your reaction time is quicker, and your strength is at its peak.

In a Chronobiology International study of runners, researchers investigated whether or not athletes were more easily tired during repeated exercise in the afternoon or the morning. They administered a repeated sprint test to athletes at different times of the day and found that the athletes experienced higher initial power output in the afternoon.

In another Chronobiology International study of competitive cyclists, researchers confirmed that there is a diurnal variation in anaerobic power output. They found that power output values were higher in the evening than in the morning.

The Best Time for You

How does all this research relate to the average athletic person? If you do anaerobic or speed workouts (on the track, in the pool, or in the gym; and usually do so just once per week), you will likely get more out of them if you do them in the afternoon. But for less strenuous workouts, the time of day has no effect on performance.

Therefore, the best time is:

• When you can fit it in—Strive for at least 30 minutes of exercise on most days of the week. People who exercise in the morning are typically more faithful to their exercise routine. Often as the day goes on, responsibilities mount up, time gets short, and exercise drops off the list.
• When your partner can do it—People who workout with a partner are more likely to stick with their routines. Knowing that someone is depending on you makes you more accountable. And having someone to talk to makes it more enjoyable.
• When you will be racing—If you are training for a marathon that starts at 7:00 am, begin all your long training runs at 7:00 to help your muscles become accustomed to exertion at that time of day.
• When you need an energy boost—Morning exercisers enjoy a jump start to their morning, while those who work up a sweat in the afternoon can avoid the post-lunch slump. Keep in mind that working out too close to bedtime can make it difficult to fall asleep.
• When weather permits—If you exercise outside, be careful in extreme weather. In the summer, exercise in the morning or evening to avoid the mid-day heat and humidity. In the winter, heed wind chill advisories.

You will reap many physical, emotional, and social benefits no matter what time you exercise. Find a time that works for you and make it a habit. Start every session with several minutes of warm-up—fast walking or jogging and light stretching—regardless of the time of day.