Asymmetries between legs: targeted training appears useful, but superiority remains unproven

Targeted programs compared with general training

The review brings together 11 studies conducted in healthy athletes aged 12 to 30 years. The interventions involved the lower limbs and lasted at least four weeks. Each study had to measure changes in asymmetries between legs, along with at least one physical performance outcome.

The researchers distinguished between two comparisons: individualized programs providing a greater stimulus to the limb identified as weaker versus programs training both sides equally, and unilateral training versus bilateral training. These distinctions matter: working one leg at a time does not necessarily mean tailoring training to the initial asymmetry.

The literature search covered Web of Science, PubMed and SPORTDiscus through April 2025. The dossier provides access to the PubMed abstract, not the full text.

Less asymmetry, but task-specific gains

Reductions in asymmetry were more consistent with targeted programs than with general programs, and with unilateral training than with bilateral training. However, the abstract provides no effect size to quantify the advantage.

Most interventions also improved physical performance. Targeted and unilateral programs generally produced greater gains in single-leg tasks. Conversely, bilateral training showed more favorable effects in tasks involving both legs.

The findings therefore do not identify one winning training approach for every goal. Reducing a difference between sides and improving bilateral performance are two distinct outcomes.

Injury prevention has not been demonstrated

The abstract notes that asymmetries have been associated with an increased risk of injury and poorer performance. This association is not enough to show that correcting them prevents injuries. The results reported here concern asymmetries and performance.

Protocols and measurements varied across studies, limiting generalizability. The authors call for more high-quality research to confirm the superiority of targeted approaches and establish precise recommendations. This review therefore cannot determine how much extra training volume should be assigned to the weaker leg.

What we can take away

Targeting the weaker limb appears to help reduce asymmetries in young athletes. This demonstrates neither greater improvements across all performance outcomes nor injury prevention.