Bright-light therapy appears to have helped delay the sleep/wake cycles of swimmers who were shortly to compete in the 2016 Olympic Games in Rio de Janeiro, Brazilian researchers report.

The effort was made to shift the athletes' sleep/wake cycles because it was known ahead of time that some of their Olympic competitions were scheduled to start as late as 10 p.m. or even midnight. The modulation of their sleep/wake cycles improved the athletes' reaction times, a crucial attribute for elite-level swimmers.

"The use of artificial light-emitting glasses might be a useful procedure for athletes who are competing in different time zones, or at unusual times and need to adjust their sleep/wake cycles in order to conform to the competition timetables," write João Paulo P. Rosa et al. in Chronobiology International.

Circadian rhythms have a direct influence on the body and affect such variables as muscle strength, flexibility, sensory-motor coupling and perceptual and cognitive functions, Rosa reported.

"Considering these factors, changing the sleep/wake cycle (phase delay or advance) using the light intensity and the time at which the exposure occurs can optimize athletes' performance," he said. This occurs through modulating core temperature and the secretion of melatonin, which promote higher levels of alertness in the athletes, especially "if the competition happens when physiologically it is time to sleep."

Performance of Olympic swimming teams

The study participants were 22 members of the Brazilian men's and women's Olympic swimming teams (half each men and women, mean age 24). All underwent a week of adaptation, 10 days before entering the Olympic Village. During that adaptation period, each athlete wore an actigraphy monitor.

On the second day, the participants twice took a test of their reaction times, the Psychomotor Vigilance Test (PVT), once in the morning and once after 10 p.m. They began wearing the bright-light devices (glasses that emit green-blue light) on the third day, for 30 to 45 minutes between 6 p.m. and 8 p.m.

During the adaptation period, the swimmers followed a routine of waking up and going to bed later than usual. Other strategies were also used to avoid fragmented or interrupted sleep. On the eighth day, the participants again took the PVT twice, and the actigraph monitors were recovered for collection and analysis of data. Sleep diaries supplemented the actigraphy data.

After starting bright-light therapy, the athletes slept significantly later (by 28 to 43 minutes) on days 3, 6, 7, and 8. The athletes' morning mean and minimum reaction times were significantly faster on day 8 than on day 1, as were their evening mean, minimum and maximum reaction times.

"This study is very interesting, because it involves an established method of artificial bright light to delay sleep and improve reaction time in a unique set of elite athletes at the peak of their conditioning before the Olympic Games," Dr. Mark Zielinski, who directs the Neuroimmunology and Sleep Laboratory at Harvard Medical School, in Boston, told Reuters Health by email.

"(I)t is unclear if these findings would be transferable to other sports, since the specificity of the physiological attributes necessary for peak performance in a sport can vary considerably," added Dr. Zielinski, who was not involved in the study. "Nevertheless, these findings likely are transferable to sports that require a quick reaction time, such as sprinting."