Bilateral Lower-Limb Asymmetry as a Predictor of Injury Risk in Athletes: An Updated Systematic Review and Meta-Analysis

Objectives: To systematically review and, where data permit, meta-analyze the association between bilateral lower-limb asymmetry and subsequent injury risk in athletes, updating the only prior systematic review on this question (Helme et al., 2021), which found mixed narrative results across 31 studies without quantitative pooling. Methods: Systematic review and meta-analysis, prospectively registered on OSF Registries (DOI 10.17605/OSF.IO/XWVF7). Eligible studies were prospective cohort or nested case-control studies measuring a quantified inter-limb asymmetry index and a subsequent musculoskeletal injury outcome in athletes. Risk of bias was assessed with QUIPS across six domains. Random-effects (DerSimonian-Laird) meta-analysis was performed separately by reported effect metric (odds ratio, risk ratio, hazard ratio). Results: Of 40 candidate studies, 30 met full-text eligibility; 32 contributed to narrative synthesis. Three studies reporting odds ratios pooled to OR = 4.20 (95% CI 1.88–9.39; I² = 0%); four studies reporting risk ratios pooled to RR = 2.19 (95% CI 1.13–4.23; I² = 71.5%). One hazard-ratio study (HR = 1.18, 95% CI 1.05–1.32) was reported descriptively. Remaining studies were synthesized narratively, including a large null-predominant soccer cohort and a novice-runner cohort whose sole significant finding ran opposite to the review’s overall direction. Conclusions: Higher bilateral lower-limb asymmetry is associated with greater odds/risk of subsequent injury across heterogeneous designs and sports, though effect sizes vary by testing modality and sport, pooled subgroups remain small, and evidence certainty is rated low to very low, reflecting the small number of pooled studies and, for the risk-ratio subgroup, substantial heterogeneity.