Researchers analyzed 20 years (1992 to 2011) of Major League Baseball statistics to determine how jet lag affects players. They looked at more than 40,000 games and 4,919 instances in which a team crossed two or three time zones without having the proper time to adjust their sleep schedules — the baseline for being considered “jet lagged” in the study.
And they found that players performed worse on average, most notably base-runners and pitchers.
On Monday, the detailed findings were published in the Proceedings of the National Academy of Sciences.
“Jet lag does impair the performance of Major League Baseball players,” Ravi Allada of Northwestern University, a circadian rhythms expert who led the study, said in a statement. “The negative effects of jet lag we found are subtle, but they are detectable and significant. And they happen on both offense and defense and for both home and away teams, often in surprising ways.”
First, it’s important to note that the effects were more profound when teams traveled east than west, consistent with the general effects of jet lag.
As The Washington Post’s Ben Guarino reported:
That’s because our sleep cycles need different amounts of time to readjust. It is easier, say scientists at the University of Maryland, for our neurons to cope with a prolonged day than a shortened one. Traveling west — backward in time zones — adds hours to the day, closer to the longer day most human bodies naturally prefer.
Furthermore, of those traveling east, teams playing at home suffered most. The reason isn’t clear, but as USA Today noted, “lifestyle may be the culprit. When players fly home, they often return to families and long to-do lists, both potential enemies of sleep.”
This disparity was so great, Allada said, “The effects are sufficiently large to erase the home field advantage.”
During the 20-year period, teams won about 54 percent of home games, a statistical 4 percent advantage.
But when looking at teams that had to first travel eastward to play those home games, that advantage disappeared.
Teams suffering from jet lag gave up more runs, an average of an extra .197 runs at home and .162 away per game.
Pitchers, in particular, suffered from eastward travel. They tended to give up an additional .107 (at home) or .073 (away) home runs during each game.
This might sound small, but one home run every 10 games is nothing to sneeze at. As noted in the study, these comprised 87 and 72 percent of the jet lag-induced runs.
On offense, those playing at home successfully stole .062 fewer bases and hit .162 fewer doubles. Furthermore, they had .141 fewer at-bats to even attempt those doubles.
And that’s just the tip of the statistical iceberg.
Whether jet lag can affect a specific game in a measurable way is impossible to know, but Allada speculated that it might have played a role in the 2016 National League Championship Series.
During that series between the Los Angeles Dodgers and the Chicago Cubs, Dodgers star Clayton Kershaw pitched twice. In game two, he only gave up two hits. In game six, though, he gave up seven hits and five runs.
“For game 6, the teams had returned to Chicago from LA, and this time the Cubs scored five runs off Kershaw, including two home runs,” Allada said. “While it’s speculation, our research would suggest that jet lag was a contributing factor in Kershaw’s performance.”
Of course, it should probably be noted Allada is an avowed Cubs fan.
Even before this study, the MLB has been working to alleviate player fatigue by changing several scheduling rules for 2018. As the Associated Press reported, the 162-game season will now be played over 187 days, rather than the current schedule over 183 days.