The effect of lower inter-limb asymmetries on athletic performance: A systematic review and meta-analysis

Inter-limb asymmetry refers to an imbalance in performance between the left and right limbs. Discrepancies throughout asymmetry research does not allow practitioners to confidently understand the effect of inter-limb asymmetries on athletic performance. Therefore, this review summarized the current literature using a meta-analytic approach, conforming to the Preferred Reporting Items for Systematic Review and Meta-Analyses guidelines to identify the association between inter-limb asymmetry and athletic performance. A literature search using PubMed, Web of Science and SPORTDiscus databases yielded 11-studies assessing the effect of inter-limb asymmetries, measured via unilateral jump performance, on bilateral jump, change of direction (COD) and sprint performance in adult sports players. The quality of evidence was assessed via a modified Downs and Black checklist and in compliance with the Grading of Recommendations Assessment Development and Evaluation. Correlation coefficients were transformed via Fishers z (Zr), meta-analysed and then re-converted to correlation coefficients. Egger's regression presented no significant risk of bias. Vertical jump performance was not significantly affected by asymmetry (Zr = 0.053, r = 0.05; P = 0.874), whereas COD and sprint both presented significant weak associations (COD, Zr = 0.243, r = 0.24; Sprint, Zr = 0.203, r = 0.2; P < 0.01). The results demonstrate that inter-limb asymmetries seem to present a negative impact to COD and sprint performance but not vertical jump performance. Practitioners should consider implementing monitoring strategies to identify, monitor and possibly address inter-limb asymmetries, specifically for performance tests underpinned by unilateral movements such as COD and sprint performance.