Cross-education of unilateral resistance training as a strategy to mitigate immobilization-induced neuromuscular...

Limb immobilization leads to a rapid and pronounced loss of muscle strength and size. Cross-education, contralateral resistance training of the nonimmobilized limb, has emerged as a resistance training strategy to mitigate deficit in the immobilization limb. A systematic review and three-level hierarchical meta-analysis were conducted (eight studies were included; n = 189) to quantify the effects of cross-education on strength and muscle mass during unilateral upper limb immobilization in healthy participants, examining the influence on training modality, muscle specificity, and immobilization model. Standardized mean change effect sizes (SMCR, Hedges' g) were calculated for strength and muscle size. Cross-education attenuated strength loss compared with immobilization alone (g = 0.53, P < 0.001), with effect magnitude moderated by immobilization location and training modality. Proximal immobilization yielded greater attenuation (overall: g = 0.62; eccentric: g = 0.82; concentric-eccentric: g = 0.68) than distal immobilization (overall: g = 0.42; eccentric: g = 0.34; and isometric: g = 0.63). Regarding muscle size, cross education produced a small preservation effect in the immobilized limb (g = 0.19, P = 0.01). This effect was only evident in proximal immobilization (g = 0.40) compared with distal (g = 0.06). Strong positive associations were observed between adaptations in the trained and immobilized limbs for strength (r = 0.79) and muscle size (r = 0.81). These findings indicate that cross-education attenuates losses in muscle strength and size during immobilization. However, these results should be interpreted with caution due to the varying risk of bias among the included studies.