Cross-education of upper-limb strength and muscle thickness following unilateral resistance training: a systematic review and meta-analysis

Background Unilateral limb immobilization leads to rapid declines in muscle strength and function. Cross-education has been proposed as a strategy to mitigate disuse-related strength loss, although current evidence remains largely indirect. Although widely studied in the lower limb, evidence specific to the upper limb has not been systematically synthesized.Objective To determine the effects of unilateral resistance training on contralateral strength and muscle thickness in the upper limb and to explore the potential influence of contralateral limb immobilization on the magnitude of cross-education.Methods A systematic review and meta-analysis of randomized controlled trials was conducted. Searches were performed in PubMed, PEDro, Cochrane Library, Web of Science, and Scopus from inception to January 2026. Eligible studies included healthy adults performing unilateral upper-limb resistance training compared with a non-exercise control group. Outcomes were contralateral strength and muscle thickness. Random-effects meta-analyses were performed using standardized mean differences (SMD) with 95% confidence intervals (CI). Risk of bias was assessed using the Cochrane RoB 2 tool and certainty of evidence using GRADE approach.Results Thirty-one studies involving 1,214 participants were included. Unilateral resistance training produced small but significant improvements in contralateral maximal voluntary isometric contraction (SMD = 0.42; 95% CI 0.12–0.72) and one-repetition maximum strength (SMD = 0.36; 95% CI 0.04–0.69). Subgroup analyses suggested potentially larger effects in studies involving partial or total immobilization of the contralateral limb, although based on few heterogeneous studies. No significant effects were observed for muscle thickness (SMD = 0.14; 95% CI −0.23–0.51). Certainty of evidence ranged from low to very low.Conclusion Unilateral resistance training elicits small but significant improvements in contralateral upper-limb strength without detectable hypertrophic adaptations. These findings support a predominantly neural mechanism underlying cross-education and suggest potential relevance for strength preservation strategies during periods of upper-limb disuse, although evidence is indirect.