Association of Lower-Limb Asymmetry with Falls, Physical Performance and Frailty in Older Adults: A Systematic Review

Background/Objectives: Whether lower-limb interlimb asymmetry is associated with adverse outcomes in older adults independently of bilateral strength, power or muscle mass remains unclear. This review synthesized evidence linking lower-limb asymmetry with falls, physical performance and frailty in adults aged ≥60 years from populations not defined by a unilateral neurological or musculoskeletal condition. Methods: Following PRISMA 2020, PubMed, Scopus, Web of Science and EBSCOhost were searched on 2 August 2026 for observational studies quantifying lower-limb asymmetry. Risk of bias was assessed with the Newcastle–Ottawa Scale and AXIS. Because exposure definitions and effect measures were incompatible, meta-analysis was not feasible; a narrative synthesis based on the direction of effect was conducted according to SWiM, and certainty of evidence was rated with GRADE. Results: Twenty-six studies (10,167 participants; 16 cross-sectional, 6 case–control, 4 prospective cohorts) were included. Findings for strength and power asymmetry were inconsistent, and the largest prospective cohort (n = 5347) found no association with recurrent falls. Greater muscle mass asymmetry was associated with slower gait speed in three cross-sectional studies. Selected gait and loading asymmetry measures were associated with subsequent falls and incident frailty in two small cohorts. Positive findings for falls came mainly from case–control studies with retrospective, self-reported fall ascertainment, whereas the studies at the lowest risk of bias did not confirm them. Certainty of evidence was very low for all eight exposure–outcome pairs, including muscle mass asymmetry and gait speed. Conclusions: Lower-limb asymmetry is not a homogeneous construct, and its associations, which depend on the measurement domain and outcome, should be regarded as exploratory. Current evidence does not establish the independent predictive value of asymmetry and supports neither a universal asymmetry threshold nor its use as a standalone fall-risk marker; it should be interpreted alongside bilateral muscle capacity and task demands.