Brain drain: the cost of fatigue in team sports

Every athlete is aware of the impact of physical fatigue on performance in sport. What’s becoming increasingly apparent is that mental fatigue can influence physical performance as well. That is, activities which have a high cognitive demand, yet no physical demand can still directly influence physical performance. And as modern life becomes increasingly cognitively challenging rather than physically challenging, understanding the role of mental fatigue has become increasingly important.

Mental fatigue in team sports

Much of the research on mental fatigue in sport over the past two decades has been performed in endurance sports, and consistently demonstrated that mental fatigue does impair performance. However, less work has been done in team sports, where the demands are often more intense, but shorter lived but it remains to be seen if the same dynamics are at play here – ie whether mental fatigue in the absence of physical fatigue can still directly influence physical performance in repeated high intensity exercise. The good news is that more recent research has sought to shed light on the impact of mental fatigue in team sports athletes.

In an excellent study on this topic, an international group of researchers investigated the relationship between mental fatigue and team sport performance⁽¹⁾. To do this, the researchers recruited 18 male team sport players to participate in the study. All of the participants were recreationally active and members of amateur team sport clubs, with a participation history of at least three years. And while not elite athletes, they were very experienced with an established training background. The researchers’ aim was to determine the precise influence of mental fatigue on physical performance during tests that were representative of the actual physical challenges athletes face in team sport competition.

What they did

The athletes firstly performed a baseline testing battery to determine their physical abilities. On separate dates, they then performed either a mentally fatiguing test or a control condition:

• During the mentally fatiguing task, the subjects performed what is known as a ’Stroop Test’ (see video clip below) where they had to identify incongruent words and colors.  This has been shown to be a difficult mental task.
• In the control condition, the subjects watched a documentary about cars – ie presenting no particular mental demands.
• The initial baseline testing was then repeated after both interventions to determine the influence of mental fatigue on performance.

STROOP TEST VIDEO

To help account for confounding factors that could reduce the accuracy of the results, the researchers used a ‘within subjects’ study design.  Because the intervention took place during a single day, all subjects performed both the experimental protocol and as well as the control protocol. At least ten days separated the two interventions to ensure that there was no cross influence between the two.

A series of physical and psychological tests were performed to assess physical performance and the amount of mental fatigue. Prior to performing the experimental or control condition, subjects were tested for their vertical jump height capacity, performed a psychomotor vigilance test, and filled out a visual analogue mental fatigue scale. As the name implies, this test measures perception of mental fatigue. The jump test is a simple to way to measure physical abilities, whereas the psychomotor vigilance test uses reaction times to assess cognitive state. Following the experimental conditions, the subjects repeated the psychomotor vigilance and jump tests, as well as the visual analogue mental fatigue scale.

The subjects then performed a repeated sprint ability test and a repeated jump ability test to measure their capacity to repeatedly perform high intensity exercise. Performance was measured, as well as blood lactate prior to and following the tests. In addition, a motivation questionnaire was given prior to the performance tests, and the NASA-TLX questionnaire was given after. This test measures, effort, frustration, and mental and physical demand. This was carried out because while the researchers wanted to know whether mental fatigue affected performance, they also wanted to know which internal changes lead to changes influencing performance, and whether those changes were physical or psychological.