Time-Out for Exercise!

"Human exercise performance is better in the evening compared to the morning, as [athletes] consume less oxygen, that is, they use less energy, for the same intensity of exercise in the evening versus the morning."
"It means, for example, if a person needs to go for a run, he will reach exhaustion earlier in the morning compared to the evening."
"In other words, he will be able to run for a longer duration in the evening compared to the morning under the same running conditions."
"If you wish to break the world record, or  your personal time, I assume [evenings would be better]."
Gad Asher, researcher, Department of Biomolecular Science, Weizmann Institute of Science

"We identified that time of exercise is critical in order for exercise to be beneficial [in metabolizing sugar and fat]."
"Circadian rhythms dominate everything we do [the internal mechanism influencing human cycles of sleep, awakening, eating, etc.]"
"At least fifty percent of our metabolism is circadian, and fifty percent of the metabolites in our body oscillate based on the circadian cycle. It makes sense that exercise would be one of the things that's affected."
"There is a time for exercise, resting or food intake. The metabolic cycles are not adapted to respond to external stimuli the same way at day or night."
Paolo Sassone-Corsi, director, Centre for Epigenetics and Metabolism, University of California, Irvine 

"Exercising late at night may interfere with sleep as it tends to energize you and enhance alertness, although some people like to exercise at the end of the day to help relieve the stresses of the day and prepare for evening activities, which is fine."
"Morning exercise has the advantage that no matter what else happens during the day, you have incorporated your physical activity. It also increases alertness and helps cognitive functioning."
Edward R. Laskowski, co-director, Mayo Clinic Sports Medicine

Two studies, geared to studying basically which time of day exercise is undertaken is more beneficial shed some light on the whys and wherefores that can be extremely instructive to those who puzzle over the issue, both for efficient use of time and for maximizing both fitness and health opportunities.
One paper's focus resulted on the understanding that morning exercise may serve to activate certain genes in muscle cells increasing their capacity to metabolize sugar and fat.

This result has great meaning to those suffering from Type 2 diabetes or who are overweight -- or both -- since middle age-plus-overweight often triggers diabetes onset, alongside sedentary behaviour. In the opposite direction, an evening workout using less oxygen makes workouts more efficient, leaning toward an improvement of athletic performance -- an obvious benefit for serious competitors.

Dr. Asher's research group placed mice on treadmills at various times of day to study their exercise capacity at different intensities and regimens. Overall exercise performance was found to be improved -- about 50 percent on average -- during 'mouse evening' as opposed to morning. Another study group led by Dr. Sassone-Cosi placed mice on treadmills as well, taking a different approach, looking at the alterations in muscle tissues post-morning workouts with a particular attention to glucose breakdown and fat burning.

When they analyzed tissue, it was to discover that exercise appeared to provide the most beneficial effects on metabolism during the mouse equivalent of what represents late morning for human exercise. The conclusion that Dr. Sassone-Corsi reached is that the process relies on a protein, HIF1-alpha, directly regulating the body's circadian clock. Elite, serious athletes such as marathoners, basketball and soccer players looking for a competitive edge might select evenings to train or compete.

If concern for weight and controlling blood sugar levels is the motivating factor for exercise -- unconcerned with shaving a minute or two from marathon time -- these individuals might decide for morning exercise, when post-workout cell responses influencing metabolism are much more engaged. With this, Jonas Thue Treebak agrees, as associate professor at the Nova Nordisk Foundation Centre for Basic Metabolic Research, University of Copenhagen, co-author of a third study.

"At this point, we can only conclude that the effects of the two appear to differ, and we certainly have to do more work [research]", he states. Irrespective, however, of determining which of the choices, morning or evening time set aside specifically for exercise will work for anyone, the takeaway from all those involved in research and exercise performance is that the timing is irrelevant in actual fact, to the need to get out there at whichever time and just proceed with exercising to attain a quality lifestyle.

"[The research] tends to suggest that morning exercising before eating is helpful in terms of ensuring maximizing some of the positives effects of exercise on metabolism."
"To me, the other positive of exercising first thing is that you get it done before the day catches up with you."
"The 'do something' message is far more important than the 'do something at a specific time of the day' message."
Michael Joyner, Mayo Clinic