Comparative effects of unilateral versus bilateral training on performance adaptations: a systematic review and multilevel meta-analysis.

This study systematically compared the effects of unilateral training and bilateral training on strength, jump performance, muscle hypertrophy, sprint performance, and change-of-direction performance, and further explored potential moderators. A systematic search was conducted in PubMed, Web of Science Core Collection, the Cochrane Library, Embase, and EBSCO. Hedges' g was used as the effect size, and a three-level meta-analysis was performed under random-effects models. Subgroup analyses, meta-regression, and sensitivity analyses were conducted to explore potential moderators and examine the robustness of the findings. A total of 24 randomized controlled trials were included. Compared with bilateral training, unilateral training showed significant advantages for unilateral strength (g = 0.42, 95% CI 0.23 to 0.60, p < 0.001) and unilateral jump performance (g = 0.35, 95% CI 0.14 to 0.56, p = 0.002). In contrast, bilateral training showed a small but significant advantage for bilateral strength (g = -0.28, 95% CI -0.54 to -0.02, p = 0.034). No significant between-group differences were observed for muscle hypertrophy, bilateral jump performance, sprint performance, or change-of-direction performance. Subgroup analyses did not identify significant between-subgroup differences for unilateral jump performance or change-of-direction performance. Meta-regression did not identify any significant moderators. Unilateral training appears to be more effective for improving unilateral strength and unilateral jump performance, whereas bilateral training may be more beneficial for enhancing bilateral strength. The choice between unilateral training and bilateral training should therefore be guided by specific training goals and sport-specific movement characteristics.