Lungs peak later in day

Exercisers who are forever searching for the best time to work out might get the most out of their sessions if they hit the treadmill or gym in the late afternoon.

By studying lung capacity in 4,800 men and women, researchers found that resistance in airway passages decreases as nightfall approaches.

Consequently, participants were able to take in a greater amount of air -- as much as 15% to 20% more than other times during the day.

The participants -- all residents of Long Island, N.Y., with an average age of 55 -- were given hourly standard pulmonary function tests during typical workday hours, from 8 a.m. to 5 p.m. Subjects were asked to inhale as much air as they could in one second, then exhale into a device that measures the volume of the air expelled. Some of the men and women had normal lungs, while others had lung disease or chronic conditions such as asthma or bronchitis.

The greatest improvement in lung function overall was found from 4 to 5 p.m. Although job and family responsibilities may make it difficult to squeeze in a workout session precisely at 4 p.m., exercising around that time may also offer benefits.

“That 15% to 20% increase was higher than we expected,” said lead researcher Dr. Boris Medarov, an internist at Long Island Jewish Medical Center in New Hyde Park, N.Y.

There were more surprises. Although it was known that asthmatics often have breathing problems early in the morning, around 5 or 6 a.m., the lowest lung function was actually found to occur at noon.

Other studies and theories on exercise and circadian rhythms -- the 24-hour activity cycle that controls bodily functions such as sleep and blood pressure -- support Medarov’s results. Metabolism is faster in the afternoon, and body temperature is higher, leading to better performance.

Not every healthy exerciser may feel a marked difference if they switch from morning to afternoon workouts, said Medarov, “but it does sound more prudent to have people who have asthma and bronchitis to exercise at 4 or 5 rather than noon.”

Improved lung function could also have implications for administering medications and scheduling medical procedures, since the body may respond better at certain times of the day.

As to why lung capacity increases later in the day, Medarov said it could be linked to hormone production, or it might be a side effect of some other function.

“The evolutionary reason is questionable,” he added. “We really don’t know.”