Association between inter-limb asymmetry and endurance running performance in healthy populations: A systematic review

Abstract

Abstract Backgroundː The presence of inter-limb asymmetry in the human body has traditionally been perceived to be detrimental for athletic performance. However, a systematic review addressing and comprehensively assessing the association of asymmetry between the lower limbs and endurance running performance is currently lacking. Objective: The main purpose of this systematic review was to examine the relationship between lower inter-limb asymmetry and running performance in healthy endurance runners. The secondary objective was to identify possible avenues for further research in this area. Methodsː Pubmed, Web of Science and SPORTDiscus were systematically searched for studies investigating the relationship between lower inter-limb asymmetry and (determinants of) running performance in healthy and injury-free endurance runners. The quality of studies eligible for inclusion was assessed using the Downs and Black Quality Index Tool. Resultsː Out of 4817 articles screened, 8 studies were included in this review. The quality score of the included research varied between 5/10 and 9/10. Except from one finding demonstrating a positive association between peak ankle dorsiflexion asymmetry and running performance, all other lower inter-limb asymmetry outcome measures were either negatively (N = 16) or not significantly (N = 30) associated with running performance. Conclusionsː A high heterogeneity across study methods and outcomes was apparent, making it difficult to draw a straightforward conclusion. Despite one study showing a positive relationship, the results demonstrate that some, but not all, metrics of functional, morphological, kinematic and kinetic inter-limb asymmetry are negatively or not associated with running performance. Thus, a more extensive high-quality body of research is essential to determine whether and to what extent asymmetry between the lower limbs could affect endurance running performance as well as to establish potential trade-off values for practitioners in developing training programs.