The effect of unilateral training on contralateral limb strength in young, older, and patient populations: a meta-analysis of cross education

Background: Cross education is the contralateral strength gain following unilateral training of the ipsilateral limb. This phenomenon provides an ideal rehabilitation model for acute or chronic rehabilitation; however, previous cross education meta-analyses have been limited to a handful of studies.Objectives: The present meta-analysis aimed to (1) be as inclusive as possible, (2) compare cross education in young able-bodied, older able-bodied, and patient populations, (3) compare cross education between training modalities, and (4) detail the impact of methodological controls on the quantification of cross education.Methodology: A review of English literature identified studies that employed unilateral resistance training and reported contralateral strength results. Studies were separated to examine the effect of population, training modality, limb, sex, and familiarization on the magnitude of cross education. The percent strength gain and effect size were calculated for ipsilateral and contralateral limbs.Results: A total of 96 studies fit the predetermined inclusion criteria and were included in the analysis. The included studies were further divided into 141 units employing separate unilateral training paradigms. These were separated into young, able-bodied (n=126), older, able-bodied (n=9), and neuromuscular patients (n=6). Cross education was an average of 18% (standardized mean difference (SMD)=0.71) in young, able-bodied participants, 17% (SMD=0.58) in healthy able-bodied participants, and 29% (SMD=0.76) in neuromuscular patients.Conclusion: Cross education was present in young, older, and patient populations and similar between upper and lower limbs and between males and females. Electromyostimulation training was superior to voluntary training paradigms.