Studies Link Fatigue and Sleep to MLB Performance and Career Longevity

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June 5, 2013

Two new studies show that fatigue may impair strike-zone judgment during the 162 game Major League Baseball season, and a MLB player’s sleepiness can predict his longevity in the league.

One study found that MLB players’ strike-zone judgment was worse in September than in April in 24 of 30 teams. When averaged across all teams, strike-zone judgment was significantly worse in September compared with April. The statistical model demonstrated strong predictive value through the season.

“Plate discipline - as measured by a hitter's tendency to swing at pitches outside of the strike zone - got progressively worse over the course of a Major League Baseball season, and this decline followed a linear pattern that could be predicted by data from the six previous seasons,” said principal investigator Scott Kutscher, MD, assistant professor of sleep and neurology at Vanderbilt University Medical Center in Nashville, Tenn. “We theorize that this decline is tied to fatigue that develops over the course of the season due to a combination of frequency of travel and paucity of days off.”

Data analysis tracked the frequency with which MLB batters swung at pitches outside of the strike zone during the 2012 season. Data were sorted by month for all 30 teams and compared between the first and last month of the season. Data for each team also were compared to a statistical model, based on data from the 2006 to 2011 seasons, which predicts a linear decline in strike-zone judgment per month.

Kutscher noted that the results are strikingly consistent and seem to contradict the conventional wisdom that plate discipline should improve during the season through frequent practice and repetition.

“Teams on the East or West Coast, with good or bad records, they all follow the same pattern of worsening plate discipline,” he said. “This study suggests hitters always demonstrate the best judgment when at bat in the first month of the season.”

He added that teams may be able to gain a competitive edge by focusing on fatigue management.

“A team that recognizes this trend and takes steps to slow or reverse it - by enacting