The Relationship Between Training Load and Injury in Athletes: A Systematic Review

Background The relationship between training load and musculoskeletal injury is a rapidly advancing area of research in need of an updated systematic review. Objective This systematic review examined the evidence for the relationship between training load and musculoskeletal injury risk in athlete, military, and first responder (i.e. law enforcement, firefighting, rescue service) populations. Methods The CINAHL, EMBASE, MEDLINE, SportDISCUS, and SCOPUS databases were searched using a comprehensive strategy. Studies published prior to July 2017 were included if they prospectively examined the relationship between training load and injury risk. Study quality was assessed using the Newcastle–Ottawa Quality Assessment Scale (NOS) and Oxford Centre for Evidence-Based Medicine levels of evidence. A narrative synthesis of findings was conducted. Results A total of 2047 articles were examined for potential inclusion. Forty-six met the inclusion criteria and 11 known to the authors but not found in the search were added, for a total of 57 articles. Overall, 47 studies had at least partially statistically significant results, demonstrating a relationship between training load and injury risk. Included articles were rated as poor ( n = 15), fair ( n = 6), and good ( n = 36) based on NOS score. Articles assessed as ‘good’ were considered level 2b evidence on the Oxford Centre for Evidence-Based Medicine Model, and articles assessed as ‘fair’ or ‘poor’ were considered level 4 evidence. Conclusions Our results demonstrate that the existence of a relationship between training load and injury continues to be well supported in the literature and is strongest for subjective internal training load. The directionality of this relationship appears to depend on the type and timeframe of load measured.