Jet lag from cross-country eastward travel may affect the performance of Major League Baseball teams, according to a long-term study published Monday in .
Researchers with Northwestern University studied winning percentages and other statistics spanning 20 seasons (1992-2011) and found that teams were 3.5% less likely to win when they traveled east across at least two time zones. No significant differences were found in winning percentage when the teams traveled west.
"The direction-selective effects, at least for the home team, suggest that they are due to circadian misalignment and not due to a general effect of travel," wrote corresponding author , of the university's Evanston, Ill., campus, and colleagues.
The researchers conducted multivariate regression analysis to isolate jet lag's impact from other factors, reviewing data from the nearly 5,000 games where teams played with at least 2 hours of jet lag.
"We asked whether jet lag differentially affects the home and away teams and whether it affects all or only specific features of performance, and if so, which ones?" the researchers wrote. "Our finding that most major jet lag effects are evident after eastward but not westward travel supports the hypothesis that observed effects are due to a failure of the circadian clock to synchronize to the environmental light–dark cycles and not due to general travel effects. Nonetheless, we did observe some isolated effects of westward travel, although they had limited effects on major offensive or defensive parameters."
Home runs allowed were the key driver of the reduced winning percentage, researchers found, noting that pitch velocity and location are major homer factors. "A starting pitcher scheduled for a game in which the team is jet-lagged might travel to the game location a few days ahead of the team, to adjust to the new time zone," Allada et al suggested.
The study's findings regarding eastward travel reflected previous studies, the authors wrote, including a 10-year retrospective study of circadian advantage in baseball published in 2009. Similar findings on eastbound travel were reported earlier this year from analysis of other pro sports.
As a skeptic, Allada said, ""I was surprised that we found something, that it looked consistent with what you'd expect to see for jet lag."
Disclosures
The research was supported in part by an Advanced Research Projects Agency (DARPA) grant.
The authors did not report any conflicts of interest.
Primary Source
PNAS
Song A, et al "How jet lag impairs Major League Baseball performance" PNAS 2017; DOI 10.1073/pnas.1608847114.