If you think you’re too  busy to exercise, try this experiment: For one day, schedule a time to work out,  and then stick to it—even if you can exercise for only 10 minutes. “At the end  of the day, ask yourself if you were any less productive than usual,” says John  Jakicic, Ph.D., an exercise psychologist at the Brown University school of  medicine. The answer will probably be no—and your favorite excuse will be  gone.