“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.