Background- Anterior cruciate ligament (ACL) injury prevention programmes have shown mixed results, which may be due to differing emphasis on training components. The purpose of this study was to (1) quantify the overall and relative duration of each training component encompassed within these programmes and (2) examine the effect of these durations on ACL injury rates.Methods- A systematic review was completed and meta-analyses performed on eligible studies to produce a pooled OR estimate of the effectiveness of these programmes. Meta-regression was used to detect any relationship that programme duration and the duration of individual training components had on ACL injury rates.Results- 13 studies were included for review. Results of the meta-analyses revealed a significant reduction of injuries after preventative training programmes for all ACL injuries (pooled OR estimate of 0.612, 95% CI 0.44 to 0.85; p=0.004) and for non-contact ACL injuries (OR 0.351, 95% CI 0.23 to 0.54; p<0.001). Results of meta-regression analysis revealed that a greater duration of balance training was associated with a higher injury risk for ACL injury (p=0.04), while greater durations of static stretching was associated with a lower injury risk for non-contact ACL injuries (p=0.04).Conclusions- While ACL prevention programmes are successful in reducing the risk of ACL injury, the ideal combination and emphasis of training components within these programmes remains unclear. Evidence indicates that greater emphases on balance training and static stretching may be associated with an increase and decrease in injury risk, respectively
