Author(s): ANDRUSHKO, J., RODRÍGUEZ-COLOMA, M., SCOTT, L.D., BASCOUR-SANDOVAL, C.I., CASTILLO-VEJAR, L., CARR, J.C., Institution: NORTHUMBRIA UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 305

INTRODUCTION:
Limb immobilisation induces rapid neuromuscular decline, with early strength losses primarily driven by neural mechanisms. Cross-education, whereby unilateral resistance training yields strength enhancements in the opposite non-exercised limb, has been proposed as a countermeasure to immobilisation-induced decline. The objective of this review was to quantify cross-education effects on muscle strength and size during unilateral limb immobilisation and examine the influence of muscle group specificity and immobilisation model.
METHODS:
A systematic review and three-level hierarchical random-effects meta-analysis were conducted following PRISMA 2020 guidelines. Eight studies (189 healthy adults) involving unilateral upper-limb immobilisation with contralateral resistance training were included. Standardised mean change raw scores with Hedges' g correction were calculated. Subgroup analyses examined trained homologous muscles and proximal versus distal immobilisation models.
RESULTS:
Cross-education significantly attenuated strength loss compared with immobilisation alone (g = 0.53, 95% CI [0.34–0.73], p < 0.001), with a smaller effect on muscle size (g = 0.19, 95% CI [0.05–0.33], p = 0.01). Strength preservation demonstrated protocol specificity (eccentric: g = 0.57, p = 0.012; combined concentric-eccentric: g = 0.685, p = 0.01), muscle specificity (trained homologous: g = 0.66 vs. overall: g = 0.53), and anatomical specificity (proximal: g = 0.62 vs. overall: g = 0.53). Size preservation was significant for proximal (g = 0.40, p = 0.01) but not distal immobilisation (g = 0.06, p = 0.48), with no protocol or muscle specificity. Strong correlations existed between trained and immobilised limb adaptations for strength (r = 0.79) and size (r = 0.81).
CONCLUSION:
Cross-education effectively preserves neuromuscular strength during immobilisation, with effects predominantly neural rather than structural, evidenced by robust, multi-dimensionally specific strength preservation but smaller, less specific size effects. Clinical implementation should prioritise eccentric or combined training protocols, particularly for proximal immobilisation, with realistic expectations that strength preservation is the primary benefit while size preservation is limited to proximal regions.