The slog of the baseball season isn't easy on a player, unless he's some kind of robot. Turns out the longer teams play through the MLB's 162 games, the worse they do.

A new study tracked strike-zone judgement from September through April of last year's season, seeing how often players were willing to swing at pitches they should've let go. Out of 30 teams, 24 were worse by April, and averaged for all teams, performance was considerably worse overall. Data from the prior six seasons showed a similar downward trend, suggesting that the 2012 data wasn't a fluke.

So what was it? Fatigue, the researchers theorize: fewer days off over the course of a season along with the strain of travel. Practice throughout the season might've helped players improve, but it was outweighed by the stress of playing so many games, the researchers say.