You want to: Reset your body clock
You should try: Midafternoon
Your natural circadian rhythm can be thrown off by traveling between time zones, switching to a night shift, viewing artificial light in the evening (when the brain expects darkness) and even getting older. To find out if exercise has any effect on a broken body clock, scientists from the University of California, Los Angeles, performed a series of experiments on mice who had been bred to have a malfunctioning sense of time. They found that exercising at any time of day helped the mice get back on schedule, but it was most beneficial for the mice to run during the afternoon (or the equivalent of a rodent's afternoon)—not in the morning, as the researchers had expected. While midday workouts haven't yet been proven to be better than morning workouts for jet-lagged humans, it's not a bad idea to cancel lunch and head to the gym instead.