If you run 10Ks or swim competitively, you're used to racing against the clock. But you may be overlooking another timekeeper that plays a key role in athletic performance: your body's circadian rhythms. Nearly every physical attribute, from strength to flexibility, grows more potent over the course of a day, with most peaking between 3 and 6 P.M., says sleep expert and athletic consultant Roger Smith, D.O., of Palo Alto, California. For example, anaerobic capacity—the bursts of power we use to sprint short distances or bench press weights—is 8 percent higher around dinnertime than it is at breakfast. For the competitive-minded, an improvement of this sort could easily mean the difference between a personal best and just another sweaty workout.
Not convinced? Smith looked back at 25 years of Monday Night Football games and found that West Coast teams beat their eastern rivals 63 percent of the time. His interpretation: Since Monday night games always begin at 9 P.M. Eastern time, East Coast teams are playing well after their late afternoon prime. But West Coast players—whose body clocks read 6 P.M. at the opening kickoff—are still at their biological best.
