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Jason Giambi of the New York Yankees baseball team yawns in 2007.

The New York Yankees' Jason Giambi (left) yawns during batting practice in 2007.

Photograph by Linda Cataffo, NY Daily News Archive/Getty Images

Christine Dell'Amore

National Geographic News

Published June 15, 2011

What times major league baseball players hit the hay can predict when they'll hit it out of the park, preliminary research shows.

In a recent survey, scientists found that players who reported being morning people tended to bat best in the morning, and as the day wore on they lost their edge, said researcher W. Christopher Winter. The reverse proved true for night owls.

While people might think the new research "would be classified in the file as, Wow, you need a research study to prove that?, no one's really looked at it" before now, said Winter, medical director of the Martha Jefferson Hospital Sleep Medicine Center in Charlottesville, Virginia.

(Read about mysteries of why we sleep in National Geographic magazine.)

Everyone has natural sleep patterns called circadian rhythms, which dictate whether they rise early or late—somewhat like being right-handed or left-handed, Winter explained.

These rhythms tend to shift earlier as we age—hence the stereotype of grandma and grandpa eating their early-bird dinner special at 4:30 p.m., he said.

"Circadian timing influences every aspect of our physiology, including our behavior and physical performance," Jeffrey Ellenbogen, a neurologist at Harvard Medical School who was not involved in the new research, said by email.

"And just as genetics governs different hair color for different people—brown, red, etc.—our genes partly determine our individual differences in peak performance at certain times of day."

Early Birds vs. Night Owls at Bat

For the baseball experiment, Winter and colleagues gave 16 players from seven major league baseball teams—with an average age of 29—a standardized sleep questionnaire.

The survey, which reveals a person's circadian rhythm, had been tailored for the study. Nine players ended up being evening types and seven were morning types.

The scientists then analyzed the players' statistics from the 2009 and 2010 seasons and compared them with the games' start times.

Start times were adjusted to account for when players crossed into different time zones, Winter noted—for example, if a Baltimore Oriole traveled to Los Angeles to play in a 2 p.m. game, the start time would have felt like 5 p.m. for that player.

The results showed that early birds had a higher batting average (.267) than evening types (.259) in games that started before 2 p.m.

Similarly, night owls were better at bat (.261) than morning types in games that started after 2 p.m., said Winter, who presented his results Monday at the SLEEP 2011 meeting in Minneapolis, Minnesota. These results were repeated in later surveys not presented at the meeting.

"For everything the body does, there is a natural peak and trough," he said, and it's likely that people at the height of their wakefulness perform better athletically.

That doesn't mean a night owl is forever caged in a later sleep pattern—there are ways people can manipulate their circadian rhythms.

Because our internal sleep rhythm is determined by when we experience lightness and darkness, exposing ourselves to light earlier in the day can shift our sleep cycle earlier, for instance.

Also, drinking alcohol has been shown to disrupt sleep cycles in the same manner as jet lag, according to the National Institute on Alcohol Abuse and Alcoholism.

Harvard's Ellenbogen added: "Paying attention to these individual preferences, and the factors that influence them—like jet lag or light exposure—we can maximize our abilities, on and off the playing field."

(Take National Geographic magazine's sleep quiz.)

Sleep a "Dynamic Force"

The new sleep finding applies to nonathletes as well, Winter emphasized. For example, he suspects a study of schoolteachers' performances in the classroom may produce the same results, though it's more difficult to quantify teachers' success.

Overall, people are starting to realize that our sleep preferences and habits affect our lives and behavior much more deeply than thought, he added.

(See "Secrets of Sleeping Soundly Uncovered.")

"We really have traditionally viewed sleep as a light switch—that basically when the light is on your brain is working, things are happening, [and] when you go to sleep you turn off the switch. Nothing could be further from the truth," he said.

"Sleep is its own dynamic force—we're really starting to get to the bottom of what's going on in those eight hours, and I believe it is the foundation for the next frontier of athletic performance enhancement."

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