MENTAL FATIGUE IN SOCCER: A SYSTEMATIC REVIEW

ABSTRACT Fatigue in soccer players is traditionally investigated based on neuromuscular and metabolic factors. However, given that soccer is one of the sports that has the highest cognitive demand, it is believed that players' performance might also be influenced by the high levels of attention, and frequent decision-making required in soccer. This systematic review aimed to verify the effects of mental fatigue on physical, technical, tactical and cognitive performance of soccer players. We searched in the electronic databases Pubmed, Web of Science and Scopus, for articles published up to 30 April 2018. We included articles that used a protocol of mental fatigue through cognitive tasks performed prior to a physical or cognitive task related to soccer. Only studies that presented an experimental design with the control condition (without mental fatigue) and the experimental condition (with mental fatigue) were selected. A total of six articles met the inclusion criteria, one study by backward reference search and other through the authors' indication. The results showed smaller distances covered in physical tests, while the effects of mental fatigue on physical performance in small-sided games were not clear. In technical tests, there were more penalties in passes and less accuracy and speed when kicking the ball when players were in conditions of mental fatigue. Regarding the tactical variables, it was found that mental fatigue had a detrimental effect on the synchronization between team players and on individual tactical performance in defensive actions. In cognitive tests, based on video recordings of game play, negative effects on the players' speed and accuracy of decision-making were observed. According to the results of the literature search, it can be inferred that mental fatigue is a factor that has a negative influence on soccer performance. Level of evidence II; Systematic review.