Photo

Athletes have long sought ways to gain even a small edge that can make the difference between getting a medal and finishing in the middle of the pack, like altitude training or even performance-enhancing drugs.

Now British researchers are reporting that something completely legal and much less damaging to the body can dwarf the effects of drugs like EPO or testosterone. What really matters, they say, is whether the time of an event is in sync with an athlete’s body clock.

The most extreme example involves people who naturally go to bed late and wake up late. Even trying as hard as they can, they are as much as 26 percent slower when they sprint in the morning as in the evening. Individuals, like runners or cyclists, and people playing team sports, like soccer or football, would be affected.

“Quite a remarkable finding,” said Carlyle Smith, a circadian rhythm expert and emeritus professor at Trent University in Canada who was not involved in the research.

The results, published Thursday in the journal Current Biology, diverge sharply from those of earlier studies that found that performance peaks in the evening. The lead researcher, Roland Brandstaetter of the University of Birmingham, said the previous research had measured athletes together — those who woke early, those who woke late, and those in between. When Dr. Brandstaetter lumped his athletes together he, too, found that, as a group, they performed best in the evening. It was only when he divided the athletes into groups according to their circadian rhythms that profound differences emerged.

The study was small — the researchers tested 20 competitive field hockey players and 22 competitive squash players six times a day.

The early risers tended to wake up, on average, around 7 a.m. on weekdays and 7:30 on weekends; intermediate risers got up about 8 on weekdays and 9:10 on weekends; and the late risers awoke about 9:30 on weekdays and 11 on weekends. The researchers evaluated their performances with measures involving sprinting tests and, for the squash players, a test of concentration and alertness in which the athletes had to hit a ball into a small area.

The early risers had their peak performances at midday, the intermediate group did best in the afternoon and the late risers did best in the evening. Everyone did the worst at 7 a.m.

Dr. Brandstaetter said some earlier studies had examined as many as 20 athletes while others had as few as six to eight.

Scientists not involved in the research said the findings make intuitive sense. “Every athlete knows that there are times of day when they perform best,” said Dr. Benjamin D. Levine, the director of the Institute for Exercise and Environmental Medicine at Texas Health Presbyterian Hospital in Dallas.

But researchers also said that the large differences in performance that the study found needed to be replicated. Dr. Levine said future studies should also involve larger groups of elite athletes and more rigorous performance tests that accurately reflect each athlete’s chosen sports.

Kenneth P. Wright Jr., the director of the sleep and chronobiology lab at the University of Colorado, Boulder, said the findings seemed consistent with what is known about biological clocks. Researchers have long known that an individual’s natural circadian rhythm controls body temperature, heart rate, reaction time and concentration, so it might be expected that individual biological clocks would affect athletic performance.

The good news for athletes is that circadian clocks can be tweaked. Dr. Brandstaetter says he deliberately alters his depending on what he plans to do, adjusting factors like light, activity and meal times. He normally does not get up early or late, but somewhere in between. But he makes himself an early riser for work and becomes a late riser when he is on vacation. He is now working with athletes, doing what he calls “circadian coaching.” The idea is to change the natural biological clocks of those who are naturally late risers when their sporting events — like marathons — start early in the day.

Of course, there is more to athletic performance than physiology, exercise researchers noted. “One of the biggest problems in athletic performance research is that we cannot replicate the highly motivated and competitive situations in the laboratory,” said Hirofumi Tanaka, an exercise researcher at the University of Texas in Austin.

Yet, he adds, “there is no question that circadian rhythms affect sports performance.” That is one reason athletes worry about jet lag, which can disrupt circadian rhythms “and become a performance killer.”

As for coaches and team owners, Dr. Smith said, “It would be handy to know the phenotype of all of your team members. You could predict who would be playing well at various times of day.”

“Chronomoneyball,” he quipped.