Playing at least 81 games on the road, sometimes thousands of miles from home and in a different time zone, will eventually have an effect on even the most fit professional baseball player, but is there a correlation between distance (and direction) traveled and performance?

That was the question that researchers from Northwestern University hoped to figure out after analyzing data from 20 Major League Baseball seasons — from 1992 to 2011 — comprising more than 46,535 Major League Baseball games, for effects of “travel-induced circadian misalignment” — aka jet lag — on performance.

For the study, published this month in Proceedings of the National Academy of Sciences, researchers determined jet lag by looking at the number of time zones crossed and the number of days since travel, and then defined jet lag as those games where a team had at a two-hour jet lag, that is, where a team had traveled across at least two time zones. Using those parameters, researchers found 4,919 instances of teams having at least two hours of jet lag.

Related from Consumer Reports: How To Beat Jet Lag

The study’s authors also accounted for “potential confounding variables,” such as home-field advantage and team effects.

“Because home teams were less often jet lagged, i.e., upon return travel home, differences attributed to jet lag could be due to home-field advantage, i.e., the general advantage a team displays at home,” researchers noted.

In general, the negative correlation between jet lag and a team’s winning percentage was stronger when teams traveled eastward than when they flew west, researchers found. Which makes sense, they say, as it’s “consistent with the fact that the intrinsic human circadian period is slightly longer than 24 hours, thus making it easier to adjust to westward travel, which lengthens the day, than to eastward travel.”

That said, there was only a significant negative correlation with team slugging percentage — total bases per at bat — for home teams, not away teams.

“Home-team eastward travel, but not westward travel, significantly reduced doubles, triples, and stolen bases, and increased double plays,” researchers write.

While only home teams saw a significant effect on their offensive performance, both home and away teams’ defensive efforts struggled in the face of jet lag from eastward travel, primarily in the form of giving up more home runs than non-jet lagged teams, researchers found.

“Pitching location and velocity appear to be important for determining the probability of giving up a home run relative to a swinging strike,” researchers note. “Thus, we hypothesize that jet lag, particularly in the eastward direction, may adversely affect these aspects of pitching which in turn impact home runs allowed.”

Despite the findings that most major jet-lag effects are evident after eastward but not westward travel, researchers said they did observe some “isolated effects of westward travel, although they had limited effects on major offensive or defensive parameters.” For example, stolen base attempts.

As for why they detected a more “robust” effect of jet lag on the home team offense rather than the away team, researchers speculate that one possibility is that the away team has a more structured daily schedule when away from home than does the home team when returning home. The home team players can go to their houses and rest, for example, while the away team is just hoping the hotel’s beds aren’t excessively uncomfortable.

That difference might not be evident on defense because pitchers — especially starting pitchers who play every fifth day — have a more structured schedule leading up to their start irrespective of whether they are home or away, researchers explain.

“The results on the effect of jet lag on home runs allowed suggest that teams may want to change their travel protocol to mitigate this effect,” researchers note. That might mean having your starting pitcher travel to the game location a few days ahead of time, they suggest, to adjust to the new time zone.

“Taken together, these quantitative high-resolution data reveal a surprising specificity in the effect of circadian misalignment on athletic performance,” the study’s authors write.

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