It is commonly touted around the gym that morning workouts are best. That seems like bad news for night owls and the large number of people who fit their physical activity in after clocking eight hours at the office.
This is a gray area, in fact. When fitness professionals toss around this notion, are they referring to “before breakfast,” “after breakfast” or simply the morning hours?
In November 2010, The Journal of Physiology published a study that concluded a pre-breakfast workout improves the effectiveness of nutrients and hormones linked to metabolism. During the study, researchers compared three groups of men, feeding each group high-fat, high-carbohydrate meals throughout each day. One group exercised prior to breakfast, the other after breakfast and the other not at all. The group who exercised before breakfast saw vast improvements in their metabolism compared to the other two groups, in which no notable changes in metabolism were observed. It should be noted that this study observed this effects on men consuming a high-fat, high carbohydrate diets – if you have significant challenges controlling your diet, or when the holiday season rolls around, the morning is your best bet.
Researchers reexamined the phenomenon of the morning workout and published the results in the February 2011 issue of the Strength and Conditioning Journal. This study observed two groups of male cyclists, one group exercised following an overnight fast –before breakfast – while the other group exercised following a meal. The researchers observed increased use of fat and protein among the pre-breakfast exercisers, meaning they burned through valuable muscle tissue in addition to fat. The post-meal exercisers primarily burned fat, but in the same amounts as those who worked out prior to breakfast. In the discussion following the study, researchers suggested that the equal amounts of fat burned may be due to the energy depletion that occurs in exercisers who lack fuel (i.e, a pre-workout meal) to keep them going throughout the activity.
In 2011, the Department of Exercise Physiology at IA University in Iran, set out to determine if physical activity in the morning was more beneficial than physical activity in the afternoon. The results were quite interesting. This study observed both lean and obese females, who exercised at 8am and 4pm. Following each exercise session, researchers measured the aerobic function and cortisol levels of the participants. Both participants saw significant increases in cortisol, following the morning and afternoon activity, while aerobic function improved by 13.8 percent in lean subjects in the morning and only 5.9 percent for obese subjects. Cortisol is secreted in response to stress and is notorious for slowing metabolic rates, increasing fat storage and inducing cravings for fat and sugar. Researchers explained that these results suggest that physical activity in the morning is not optimal for those that find early rising stressful, i.e., night owls. In an effort to minimize secretion of cortisol, schedule physical activity during a time of day that suits your circadian rhythm best.
All of these studies seem to offer conflicting information, but when you carefully examine the parameters of each study, results may vary. In the 2010 study, the subjects were average males who consumed very high-fat, high carbohydrate meals, while in the February 2011 study, the subjects were fit athletes. Your BMI and diet weigh heavily on your results, as does your circadian rhythm – the night owl vs. the early bird. Many people suggest a morning workout because you are less likely to skip the session in favor of dinner with friends or happy hour or even late meetings.
Bottom line – you have to choose a schedule that works for you because consistency is the key to results, not the time of day.