Jet lag impairs performance of Major League Baseball players

A new Northwestern University study of how jet lag affects MLB players traveling across just a few time zones finds that when people, in this case Major League Baseball players, travel in a way that misaligns their internal 24-hour clock with the natural environment and its cycle of sunlight, they suffer negative consequences.

"Jet lag does impair the performance of Major League Baseball players," said Dr. Ravi Allada, a circadian rhythms expert who led the study. "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."

In a study of data spanning 20 years and including more than 40,000 games, the researchers identified these effects of jet lag on player and team performance:

• The offense of jet-lagged home teams is much more affected than that of jet-lagged away teams. Surprisingly, in terms of offensive performance, jet lag from eastward travel had significant negative effects on home teams (after returning from a road trip) and much less of an effect on away teams.
• Negative effects on offense are related to base running. The negative effects on the home team's offense were related to base running, such as stolen bases, number of doubles and triples, and hitting into more double plays.
• Both home and away teams suffer on defense, specifically by giving up more home runs. With defensive performance, strong effects of eastward jet lag were found for both home and away teams, primarily with jet-lagged pitchers allowing more home runs. "The effects are sufficiently large to erase the home field advantage," Allada said. Besides home runs allowed, few other effects were seen on pitching or defense.
• There is a difference between traveling east and traveling west. Most significant jet-lag effects were generally stronger for eastward than westward travel. "This is a strong argument that the effect is due to the circadian clock, not the travel itself," Allada said.

The study, "How Jet Lag Impairs Major League Baseball Performance," will be published the week of Jan. 23 in the journal Proceedings of the National Academy of Sciences (PNAS).

Allada and his team, Alex Song (first author) and Thomas Severini, used an unprecedented amount of MLB data (from 1992 to 2011), which gave the researchers the statistical power to identify the effects of jet lag on offensive and defensive performance metrics. The researchers considered if teams were traveling east or west; if the team was home or away; and the team itself.

They also looked at the number of hours players would be jet-lagged, based on the number of time zones traveled across, to determine which games were "jet-lag games" and which were not. (The human body clock can roughly shift about an hour each day as it synchronizes to the new environment.) If players were shifted two or three hours from their internal clocks, the researchers defined them as jet-lagged.

What does all this data analysis mean going forward? With MLB spring training less than a month away, Allada has some advice based on his research.

"If I were a baseball manager and my team was traveling across time zones -- either to home or away -- I would send my first starting pitcher a day or two ahead, so he could adjust his clock to the local environment," Allada said.

Allada provides an example from the 2016 National League Championship Series illustrating the potential impact of jet lag on player performance. In game 2, Los Angeles Dodgers' ace Clayton Kershaw shut out the Chicago Cubs, giving up only two hits, but game 6 was a different story.
"For game 6, the teams had returned to Chicago from LA, and this time the Cubs scored five runs off of Kershaw, including two home runs," Allada said. "While it's speculation, our research would suggest that jet lag was a contributing factor in Kershaw's performance."

More sprints in top-class football necessitates new and individualized training routines

Today's top-class football is characterised by more short sprints than in the past. In English Premier League, high-intensity running has increased by 50% in the last 10 years, presenting new challenges to the players in terms of fatigue resistance and ability to recover quickly. The change has also resulted in greater variation in the tempo of matches, and this new pattern calls for revised training routines. This is the conclusion of new research from the University of Gothenburg and the University of Southern Denmark.

The study in question is based on an extensive amount of data. A research team, consisting of Dan Fransson and Magni Mohr, exercise physiology researchers at the Department of Food and Nutrition, and Sport Science, University of Gothenburg, and Professor Peter Krustrup from the University of Southern Denmark, watched 62 football matches played 2010-2012 and made 1 105 observations of 473 players from 24 different Premier League teams.

The results show that, compared with in the past, modern top-class football is characterised by more high-intensity sprints followed by a substantially lower tempo. Repeated bouts of high-intensity running for 1-5 minutes are followed by a historically low intensity for up to 5 minutes. Thus, a player's activity level during a match tends to alternate between two extremes, compared with the traditionally more steady match tempo.

Training Should Be Adapted to the New Pattern

The analysis points to significant differences in fatigue and recovery patterns among players. Some players can exhibit four times as much high-intensity running as others in one and the same match.

'This indicates that in order for players to maximise their potential and avoid injuries, they need more individualised training depending on position played. All players shouldn't train in the same way,' says Fransson.

Central defenders stand out from the other playing positions. These are the only players whose running did not decrease after the most intense 1-2-minute periods.

'The reason for this is simply that central defenders face the lowest demands of all players except goalkeepers when it comes to high-intensity running. They have the longest recovery periods between the intense phases of a football match,' says Fransson.

Could better eye training help reduce concussion in women's soccer?

With the ever-growing popularity of women's soccer, attention to sports-related concussions is also a growing concern, as the act of heading the ball is thought to contribute to increased incidence of concussion. 

"Current evidence shows that high school female soccer players incur a higher concussion rate than males," says Joe Clark, PhD, professor in the Department of Neurology and Rehabilitation Medicine at the University of Cincinnati College of Medicine. "While this is often attributed to gender differences in physical build or neck muscle strength, our study suggested that there might be other behaviors such as field awareness that are contributing factors that result in these higher concussion rates."

Researchers working with Clark observed that in photographs of female soccer players during play, the players often had their eyes closed while heading the ball. They wanted to quantify whether female athletes closed their eyes more frequently than male counterparts, as a first step toward determining if less visual awareness might expose players to a higher risk of injury. Their results of the first part of this study are have been published in the online version of Medical Hypotheses.

Through an analysis of Google images of soccer headers by both male and female players in active game play, 100 images of each gender were reviewed and categorized. Some images showed more than one athlete participating in the header, what some people may call a 50-50 ball.

Of 170 females identified in the photos, 90.6 percent of them were shown to have their eyes closed during play. By comparison, 79 percent of male players had their eyes closed, of the 170 male athletes evaluated in the photos. 

These findings indicated that female players were more likely to close their eyes at the act of heading the ball, versus males. Vision training methods in other concussion-prone sports like football work to train the athletes to use visual tactics to be aware of the ball and aware of other players prior to a hit something the researchers refer to as "eye discipline." 

It is felt that better eye discipline may account for the difference in concussion rates between males and females. "In other studies, vision training has successfully reduced the rates of concussion in college football athletes; overall lack of visual awareness in a contact sport may increase the risks of concussion. Therefore vision training and better eye discipline may decrease concussion rates." 

Clark, who works with high school and college-level athletes on vision training techniques to improve their awareness in avoiding hits on the field, says that with practice, athletes can learn to play safer. "The startle reflex, or blinking or closing one's eyes upon a perceived risk, can be suppressed through training and coaching. So it is possible that training to improve eye discipline and maintain control of ball handling, may help mitigate concussions in soccer players heading the ball," he says.

Hagar Elgendy, a medical student at the UC College of Medicine, and a co-author of the study, has been involved with the sports medicine research at UC for the past few years. "Concussion in sport has gained much attention recently. It was exciting and interesting to be involved in this project and to propose a hypothesis for the greater concussion incidence in the high school athletic setting for females over males." Elgendy, along with her sister, Hanna Elgendy, worked to obtain and analyze the Google images for the study.

Clark says, "We hope to follow up with larger future studies as to whether eyes closed upon impact correlate with higher rates of concussion, to validate this hypothesis."