A systematic review on methodological variation in acute:chronic workload research in elite male football players

Objectives: To investigate and evaluate the methodological variation in research on acute:chronic workload ratio (ACWR) and injury in elite male football players.Methods: Relevant literature was electronically searched on PubMed, Web of Science, ScienceDirect, and Embase. Additional literature was obtained from studies' bibliographies and authors. Cohort studies investigating the effects of ACWR on male elite footballer injuries were included. Information regarding study population, time frame, protocol, injury classification, and statistical analysis were elucidated.Results: Database searches led to 2,689 articles. After full text screening, twelve articles remained. All studies were of poor quality. Five studies had GPS-derived workload measures with consideration of running intensity zones, though little consensus over zone thresholds were found. Nine studies incorporated rated perceived exertion data; heterogeneity in exposure type and data collection timing was observed. All studies applied rolling average ACWRs, exploring 1:2, 1:3, and 1:4-week load ratio windows. Differences in data grouping, inference or regression analysis, and other statistical methods were noted.Conclusion: Existing literature displayed methodological heterogeneity. Future studies should consider consulting guidelines for developing prognostic studies and further examine causal links between workload and injury. From that basis, decisions around ACWR definitions, workload measures, and statistical methods may be more appropriately made.