Studies link fatigue and sleep to MLB performance and career longevity

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 fatigue-mitigating strategies, especially in the middle and late season, for example - can gain a large competitive advantage over their opponent,” he said. “This may have already occurred, as the San Francisco Giants - an outlier in the study in that their plate discipline improved during the 2012 season - went on to win the World Series.”

The research abstract was published recently in an online supplement of the journal SLEEP, and Kutscher will present the findings Tuesday, June 4, in Baltimore, Md., at SLEEP 2013, the 27th annual meeting of the Associated Professional Sleep Societies LLC.

Another study found a significant and profound relationship between the sleepiness of a MLB player and his longevity in the league. As baseline self-reported scores of sleepiness on the Epworth Sleepiness Scale increased, the likelihood that a player would be in the league three seasons later decreased linearly. For example, 72 percent of players with a baseline ESS score of 5 were still in the league at the follow-up point, compared with only 39 percent of players with an ESS score of 10 and 14 percent of players with an ESS score of 15.

“We were shocked by how linear the relationship was,” said principal investigator W. Christopher Winter, MD, medical director of the Martha Jefferson Hospital Sleep Medicine Center in Charlottesville, Va. “It is a great reminder that sleepiness impairs performance. From a sports perspective, this is incredibly important. What this study shows is that we can use the science of sleep to predict sports performance.”

Prior to the 2010 season, ESS data were collected from a random selection of 80 MLB players representing three teams. This study group doubled the sample size of Winter’s pilot study, which he presented last June at SLEEP 2012. Player status three seasons later was determined on Dec. 16, 2012. A player who was demoted to a lower league, unsigned, or no longer playing was deemed “inactive.”

Winter added that teams easily could implement sleepiness screening as part of their player evaluation system.

“I can envision simple questions about sleep being a part of the battery of tests professional organizations use to evaluate prospects,” he said.

He also noted that players and their teams could benefit tremendously if a sleep specialist diagnoses and treats the condition causing a player to experience excessive daytime sleepiness.

“That player may suddenly become far more valuable,” Winter said.

The research abstract was published recently in an online supplement of the journal SLEEP, and Winter will present the findings Monday, June 3, in Baltimore, Md., at SLEEP 2013, the 27th annual meeting of the Associated Professional Sleep Societies LLC.

Study challenges notion that umpires call more strikes for pitchers of same race

A University of Michigan study challenges previous research that suggests umpire discrimination exists in Major League Baseball.

The study, a collaboration between researchers at U-M and the universities of Illinois and Florida, looks deeper into the controversial argument over whether MLB umpires discriminate by calling more strikes for pitchers of the same race. It found little statistical evidence to support that claim, said Jason Winfree, associate professor of sport management at the U-M School of Kinesiology.

Winfree and co-authors Scott Tainsky of Illinois and Brian Mills of Florida, analyzed millions of pitches between 1997 and 2008 and ran the data through various statistical models. Their results suggest that findings of discrimination were questionable.

A draft of the earlier study that initially found evidence of discrimination was released in 2007 and published by the American Economic Review in 2011. National media reported on both the draft of the study and on its later publication.

In the U-M study, Winfree and his co-authors analyzed both their own data as well as that of the previously published study, but did not get consistent results when using different statistical methods and variables.

"Based on what we found, it's(discrimination) certainly not conclusive, and we could make an argument that there's actually reverse discrimination if you look only at averages," Winfree said. "Our point is (that) with something like this you want to look at the data a lot of different ways and see if you get a consistent result each time with each method. It's a pretty bold claim to say there is racial discrimination."

Winfree and colleagues found that the only specifications that suggested discrimination were when the analysis treated pitchers as completely separate players when pitching in stadiums where umpires were monitored. This seemed to drive much of the findings in the earlier study, they said.

The U-M study and others that look at discrimination in sports are significant not only for sports fans and franchises, but because it's very difficult to test for discrimination in most other occupations, Winfree said. However, because professional sports keep such detailed statistics, discrimination or lack of it is more quantifiable.

"This is a place where it's easy to test for discrimination, and if you find it here, it might be present in other work scenarios where you can't really test it," Winfree said.

The issue of discrimination among referees and umpires has raised debate in other sports as well. For instance, in 2010 the Quarterly Journal of Economics published a study that suggested racial bias among referees in the NBA.

The U-M study, "Further examination of potential discrimination among MLB umpires," appears online in the Journal of Sports Economics.