Exercise best in late afternoon.

• Position: Circadian Rhythms

Circadian rhythms, the body's biological processes that repeat in 24-hour cycles, may have a significant effect on a person's lung function and, ultimately, help determine the best time of day for exercise and the administration of medications and medical procedures. In a study by Boris I. Medarov, a physician at Long Island Jewish Medical Center, New Hyde Park, N.Y., lung function was found to have a natural circadian rhythm, where it is at its peak during the late afternoon hours and at its lowest around midday.

"Circadian rhythms regulate our biological cycles for sleep, activity level, metabolism, and many other processes through our body's exposure to sunlight and darkness," explains Medarov. "Our study finds that lung function has its own rhythm that may govern how much energy we exert throughout the day and the best times to engage in certain activities."

The study investigated how lung function fluctuated throughout the working hours of 8 a.m.-5 p.m. Results were compared within nine time intervals, and showed that patients' overall airway resistance was at its most prominent around 12 p.m. but reached its minimum between 4-5 p.m.

"We often associate the end of the workday with being tired and less motivated for...