The influence of age on the effectiveness of neuromuscular training to reduce anterior cruciate ligament injury in female athletes: A meta-analysis

Background: In female athletes, sports-related injuries to the anterior cruciate ligament (ACL) increase during adolescence and peak in incidence during the mid- to late teens. Although biomechanical investigations indicate that a potential window of opportunity exists for optimal timing for the initiation of integrative neuromuscular training (NMT) in young female athletes, the influence of the timing of initiation of these programs on the efficacy of ACL injury reduction has yet to be evaluated. Hypothesis/Purpose: The purpose of the current report was to systematically review and synthesize the scientific literature regarding the influence of age of NMT implementation on the effectiveness for reduction of ACL injury incidence. The hypothesis tested was that NMT would show a greater effect in younger populations. Study Design: Meta-analysis; Level of evidence 1 a. Methods: Data were pooled from 14 clinical trials that met the inclusion criteria of (1) number of ACL injuries reported; (2) NMT program used; (3) female participants were included; (4) investigations used prospective, controlled trials; and (5) age of participants was documented or was obtainable upon contact with the authors. A meta-analysis with odds ratio (OR) was used to compare the ratios of ACL injuries between intervention and control groups among differing age categorizations. Results: A meta-analysis of the 14 included studies demonstrated significantly greater knee injury reduction in female athletes who were categorized in the preventive NMT group compared with those who were in the control group (OR:0.54; 95% confidence interval [CI]:0.35, 0.83). Lower ACL injuries in mid-teens (OR 0.28; CI:0.18, 0.42) compared with late teens (OR 0.48; CI:0.21, 1.07) and early adults (OR 1.01; CI:0.62, 1.64) were found in participants undergoing NMT. Conclusion: The findings of this meta-analysis revealed an age-related association between NMT implementation and reduction of ACL incidence. Both biomechanical and the current epidemiological data indicate that the potential window of opportunity for optimized ACL injury risk reduction may be before the onset of neuromuscular deficits and peak knee injury incidence in female athletes. Specifically, it may be optimal to initiate integrative NMT programs during early adolescence, before the period of altered mechanics that increase injury risk.