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This systematic review was aimed at identifying the psychometric properties of field-based tests for assessing physical fitness in soccer referees. Electronic databases were searched up to May 2020 for studies that informed about the reliability and/or validity of at least one field-based physical fitness test for soccer referees. A total of 13 studies analysed the psychometric properties of the field-based physical fitness tests proposed by the Fédération Internationale de Football Association (FIFA) (aerobic endurance, n = 8; anaerobic endurance, n = 3; and speed, n = 8), while seven investigations focused on field-based physical fitness tests specifically designed for assessing aerobic endurance (n = 1) or change of direction (COD) (n = 6). According to the observed reliability and validity values, the Assistant Referee Intermittent Endurance test (ARIET), the 50-m sprint test and the Modified Agility test (MAT) seem, respectively, the best available options for assessing aerobic endurance, speed, and COD in soccer referees. Future investigations should consider the lack of research focusing on assistant and female referees. Further studies on the psychometric properties of anaerobic endurance and short distance speed tests are also needed. [ABSTRACT FROM AUTHOR]

The aims of this study were to identify the key external and internal load variables in professional futsal through principal components analysis (PCA), and analyse the physical performance required by the players in official matches. Data were collected from 14 female players during 10 matches using WIMU PROTM. The PCA selected a total of 22 variables as key indicators of players' load. Specifically, these variables were represented by five principal components. However, a novel finding was that different components were extracted when the analysis was carried out by full match (68.83% of total variance), first half (69.81% of total variance), or second half (65.96% of total variance). Also, this study found that the players decreased their physical performance during the second half. Based on these results, this study may help optimize performance and reduce the injury risk. Performance should not be only analysed considering the full match external/internal load but also specifying by match halves. This is explained by the fact that there were variables that made up the principal components in the first half, but not in the second half or full match. Finally, coaches should adopt training strategies which deal with the decrease in physical performance during the second half. [ABSTRACT FROM AUTHOR]