Contralateral effects of unilateral resistance training: a meta-analysis

Area of Science:

• Exercise Physiology
• Human Movement Science
• Sports Science

Background:

• The phenomenon of 'cross-education' suggests unilateral strength training enhances contralateral limb strength.
• Previous studies have yielded inconsistent results, necessitating a quantitative synthesis.

Purpose of the Study:

• To quantitatively synthesize evidence on the effects of unilateral resistance training on contralateral limb strength in humans.
• To provide a statistically robust answer to the physiological question of cross-education.

Main Methods:

• Systematic review and meta-analysis of randomized controlled trials.
• Inclusion criteria: voluntary unilateral resistance training, intensity ≥50% maximal voluntary strength, duration ≥2 weeks.
• Statistical pooling of strength changes in contralateral and control limbs.

Main Results:

• Seventeen studies met inclusion criteria; 13 were included in the meta-analysis.
• Pooled estimate showed a 7.8% increase in maximal voluntary strength of the contralateral limb (95% CI: 4.1-11.6%).
• This contralateral effect represented 35.1% of the trained limb's strength gains (95% CI: 20.9-49.3%).

Conclusions:

• Unilateral strength training produces statistically significant, albeit modest, increases in contralateral limb strength.
• The findings support the existence and magnitude of the cross-education effect.
• This meta-analysis provides a reliable estimate of cross-education based on pooled data from controlled studies.