Jet lag really does affect a professional athlete’s performance — just not in the way you think.

A study in the journal Proceedings of the National Academy of Sciences of the United States of America says the home team’s offense takes a beating when it comes to jet lag, based on data from more than 46,000 Major League Baseball games over the course of two decades. That means a home team is less likely to hit doubles or triples, steal bases, or avoid double plays after returning from a road trip, whereas an away team’s batters will not see much of a difference. The researchers from Northwestern University also assert that jet lag, which occurs when travel to a different time zone throws off the body’s internal clock, has an effect on both teams’ defensive playing.

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“Remarkably, the vast majority of these effects for both home and away teams could be explained by a single measure, home runs allowed,” the study says.

Traveling eastward measured up as significantly more harmful than traveling to the west when it came to the consequences of jet lag, which can include fatigue, loss of sleep, stomach issues and “impaired motor performance.”

The researchers measured jet lag by looking at how many time zones they traversed — if their body clocks were forcibly shifted two or three hours, they were considered jet-lagged.

The lead on the study, Dr. Ravi Allada, had advice for MLB coaches looking to mitigate the role of jet lag on their team.

“The negative effects of jet lag we found are subtle, but they are detectable and significant,” Allada said in a statement from Northwestern. “If I were a baseball manager and my team was traveling across time zones — either to home or away — I would send my first starting pitcher a day or two ahead, so he could adjust his clock to the local environment.”

While the data examined the performance of MLB players, the findings also have implications for other sports teams, including major leagues like the National Football League, the National Basketball Association, and the National Hockey League, all of which have teams across the U.S. and Canadian time zones. And the NFL has had some of its teams playing a few games each year in London, a five- to eight-hour time difference depending on which American coast each team is from. Next fall, eight teams from the U.S. will be playing football games in London.

Source: Allada R, Song A and Severini T. How jet lag impairs Major League Baseball performance. Proceedings of the National Academy of Sciences of the United States of America. 2017.

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