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

Key Points

1. Training one upper limb produced small but significant improvements in strength of the opposite, untrained limb. The effect was demonstrated for isometric and 1RM strength but not consistently for isokinetic strength.

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BACKGROUND & OBJECTIVE

Injury, surgery and immobilization can rapidly reduce upper-limb strength. These losses may exceed changes in muscle mass, indicating that neural factors contribute substantially to disuse-related weakness (1). When the affected arm cannot be safely loaded, training the opposite arm may provide an alternative way to limit strength loss. This phenomenon, known as cross-education, is thought to occur predominantly through adaptations within the central nervous system rather than muscle growth in the untrained limb (2,3).

This review investigated whether unilateral upper-limb resistance training improves strength or muscle thickness in the opposite, untrained arm, and whether immobilization influences the magnitude of this effect.

Injury, surgery and immobilization can rapidly reduce upper-limb strength; these losses may exceed changes in muscle mass, indicating that neural factors contribute substantially to disuse-related weakness.

Cross-education is best viewed as a temporary adjunct that may reduce strength loss, not as a substitute for later affected-side rehabilitation.

METHODS

The authors conducted a systematic review and meta-analysis of randomized controlled trials involving healthy adults. Eligible studies compared unilateral upper-limb resistance training, performed at ≥50% of maximal voluntary strength, with a non-exercise control condition. The programme had to include more

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