Dosage Effects of Neuromuscular Training Intervention to Reduce Anterior Cruciate Ligament Injuries in Female Athletes: Meta- and Sub-Group Analyses

Although a series of meta-analyses demonstrated neuromuscular training (NMT) is an effective intervention to reduce anterior cruciate ligament (ACL) injury in female athletes, the potential existence of a dosage effect remains unknown. Our objective was to systematically review previously published clinical trials and evaluate potential dosage effects of NMT for ACL injury reduction in female athletes. This study took the form of a meta- and sub-group analysis. The keywords 'knee', 'anterior cruciate ligament', 'ACL', 'prospective', 'neuromuscular', 'training', 'female', and 'prevention' were utilized in PubMed and EBSCO host for studies published between 1995 and May 2012. Inclusion criteria set for studies in the current analysis were (i) recruited female athletes as subjects, (ii) documented the number of ACL injuries, (iii) employed an NMT intervention aimed to reduce ACL injuries, (iv) had a control group, (v) used a prospective control trial design, and (vi) provided NMT session duration and frequency information. The number of ACL injuries and female athletes in each group (control and intervention) were compared based on duration, frequency, and volume of NMT via odds ratios (ORs). A total of 14 studies were reviewed. Analyses that compared the number of ACL injuries with short versus long NMT duration showed greater ACL injury reduction in female athletes who were in the long NMT duration group (OR 0.35, 95 % CI 0.23-0.53, p = 0.001) than in those in the short NMT duration group (OR 0.61, 95 % CI 0.41-0.90, p = 0.013). Analyses that compared single versus multi NMT frequency indicated greater ACL injury reduction in multi NMT frequency (OR 0.35, 95 % CI 0.23-0.53, p = 0.001) compared with single NMT frequency (OR 0.62, 95 % CI 0.41-0.94, p = 0.024). Combining the duration and frequency of NMT programs, an inverse dose-response association emerged among low (OR 0.66, 95 % CI 0.43-0.99, p = 0.045), moderate (OR 0.46, 95 % CI 0.21-1.03, p = 0.059), and high (OR 0.32, 95 % CI 0.19-0.52, p = 0.001) NMT volume categories. The inverse dose-response association observed in the subgroup analysis suggests that the higher the NMT volume, the greater the prophylactic effectiveness of the NMT program and increased benefit in ACL injury reduction among female athletes.