Jet lag affects sports performance in very specific, context–dependent ways that can influence game outcomes, according to research from Northwestern University in Evanston, Illinois. The study reviewed data from over 40,000 Major League Baseball games over a 20–year period.

"Jet lag does impair the performance of Major League Baseball players," said Ravi Allada, MD, study author and principal investigator, in a Northwestern University news release. "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."

Researchers identified the following ways in which jet lag impaired performance:

  • Jet lag effects were more significant when players had traveled eastward. "This is a strong argument that the effect is due to the circadian clock, not the travel itself," said Allada.
  • Jet lag slowed base running for home teams (after being on the road).
  • Jet–lagged pitchers, from both home and away teams, gave up more home runs.

Our circadian clock function is responsible for physiological and behavioral rhythms and is aligned with our 24–hour environment, based on light exposure. Rapid long–distance travel can desynchronize our inner clocks, causing symptoms such as poor sleep, fatigue, gastrointestinal disturbance and impaired motor performance. This is the first study to examine the effects of jet lag, or the misalignment of our biological clocks, on specific aspects of athletic performance.

The take–away for a traveler, according to Allada, is to be mindful of the potential negative effects of jet lag, even if the trip crosses only two or three time zones, and to allow time for the body to adjust to the new zone.

The study appeared in PNAS (2017; doi: 10.1073/pnas.1608847114) and is open source.