Since the analysis of worst-case scenarios (WCS) has been increasing knowledge about match demands and possible impacts for the training process, it seems important to summarize the evidence to provide useful information for the soccer community. Thus, the purpose of this systematic review was to summarize the evidence about WCS in professional soccer. A systematic review of PubMed, SPORTDiscus, and FECYT (Web of Sciences, CCC, DIIDW, KJD, MEDLINE, RSCI, and SCIELO) was performed according to the guidelines for performing systematic reviews in sport science. From the 85 studies initially identified, 12 were fully reviewed, and their outcome measures were extracted and analyzed. There was an inverse relationship between the duration of WCS windows and running output during match play. Occurrences of WCS during soccer matches were also position-dependent across studies, at least, when analyzing performance with the total distance covered variable, although different outputs were identified between women and men players. Future research should consider analyzing the impact of contextual variables (match status, team formation, and match location) on peak match values and the weight of these moderators.

Background Velocity and accelerations have been highlighted as the most important variables in soccer. However, there is a consensus gap to define different levels of effort. The purpose of this systematic review is to identify those articles that purposed a threshold to establish (i) movement intensity at different velocities using tracking systems and (ii) accelerations using inertial measurement units, classifying the justification methods. Methods A systematic review of Cochrane Library, EBSCO, PubMed, Scielo, Scopus, SPORTDiscus, and Web of Science databases was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Results From the 1983 studies initially identified, 40 were fully reviewed, and their outcome measures were extracted and analyzed. Conclusios: The 40 m maximal linear sprint test is the preferred method used in originating speed and acceleration thresholds in soccer despite recent research opted also to consider composite fitness measures such as anaerobic speed reserve. However, there is a substantial heterogeneity on locomotor testing procedures and workload zones established from these performance data while construct validity of several fitness indicators is not yet supported. Studies diverged on recommending, maybe consider or suggested avoid the use of individualized thresholds. Low sampling frequency (≤ 10 Hertz) in publications computing acceleration and deceleration demands should be also interpreted with caution. The present study collated evidence that may help conditioning professionals when processing and interpreting external load data in a soccer context.