Perhaps no sport has been subject to more statistical analysis than baseball, but neurobiologists say an important aspect of the game has been overlooked — the role of jet lag.
After crunching through data on nearly 5,000 games played over 20 seasons, the scientists calculated that jet-lagged teams were less likely to hit doubles and triples, execute sacrifice flies or steal bases. They were also more likely to give up home runs to the opposing team.
Jet lag occurs when we travel across time zones, causing our internal body clocks to go out of sync with the external clocks that govern our 24-hour days. Symptoms often include fatigue, mood changes, gastrointestinal problems and trouble with concentration, alertness and general physical function.
The more time zones you cross, the worse these problems are likely to be. Since our internal clocks naturally follow a cycle that lasts 24 hours and 11 minutes, jet lag symptoms also tend to be worse when traveling eastward (making our days shorter) than when traveling westward (making our days longer).
These disturbances can affect anyone, but
That's why Dr. Ravi Allada, who studies neurobiology at Northwestern University, and his colleagues decided to study baseball players. They combed through 46,535 games played between 1992 and 2011 and identified 4,919 in which at least one team was coping with at least two hours of jet lag. (A one-hour time difference was deemed too small to produce measurable effects.)
The researchers found that when home teams were playing under the influence of jet lag from eastward travel, their odds of winning were reduced by about 3.5%, on average. That may not sound like much, but it's in the same ballpark (so to speak) as the home-field advantage, which boosted a home team's chance of winning by 3.9%, on average.
That means that if the
Visiting teams also seemed to be hindered by eastward jet lag, but the effect wasn't quite large enough to be statistically significant. Jet lag due to westward travel did not affect the winning percentage of either home or away teams.
How, exactly, did jet lag hurt home teams that had traveled two or three time zones to the east? Offensively, they hit fewer doubles and triples and stole fewer bases. They also hit more ground balls that their opponents turned into double plays. Defensively, they performed worse (as measured by the visiting team's slugging percentage and a statistic known as fielding-independent pitching, or FIP). In particular, the home team's pitchers gave up more home runs.
Visiting teams weren't entirely immune to the effects of eastward jet lag. When traveling eastward, they hit fewer sacrifice flies and gave up more home runs (though not as many as home teams did).
There weren't that many consequences of westward jet lag, but the researchers found that visiting teams gave up more walks and allowed their opponents to get on base more often. Offsetting that to some degree, home teams gave up more triples after traveling two or three time zones to the west.
It's not clear why home teams were more affected by eastward jet lag than visiting teams, but the researchers have some theories. One is that players' schedules are more structured when they are on the road, and that might counteract some of the harms of jet lag. Another is that visiting teams are already discombobulated, and jet lag doesn't make it that much worse.
The findings should prompt baseball teams to reconsider the travel schedules of their starting pitchers, the researchers wrote. If they're going to be pitching in another time zone, perhaps pitchers should travel ahead of the rest of the team so their bodies can adjust.
Consider last year’s
"I don't necessarily want to attribute all of that change in performance to the fact that Clayton Kershaw might have been jet lagged in that game," Allada said, "but our work would suggest that at least it's a contributing factor to the change in his particular performance."
MORE IN SCIENCE