Research Reveals Unilateral Exercises Significantly Strengthen Both Halves of the Body

It's a phenomenon known as cross-education.

Unilateral exercises are becoming increasingly popular in sports performance training and for good reason.

Unilateral exercises, meaning exercises that focus on one arm or one leg at a time, possess several key advantages over bilateral movements (which target both legs or both arms at the same time). This isn't to say bilateral movements shouldn't be a part of your routine, but unilateral movements more closely mirror the explosive actions used in many athletic movements and are excellent for destroying imbalances.

But did you know that unilateral exercises also strengthen the "unused" side of the body, as well? It's true. Training one limb can cause strength gains in the contralateral (opposite) untrained limb. Essentially, you can increase strength in a limb without directly training it. It's a phenomenon known as cross-education, and a recent study in the European Journal of Applied Physiology examined just how strong this effect may be.

The researchers looked at the data from 31 studies, totaling 785 subjects. Their goal was to see the overall magnitude of effect for cross-education from unilateral exercises. Here's what they found:

  • Cross-education of strength showed a significant 11.9% contralateral strength increase
  • For the upper limb, strength increased +9.4%
  • For the lower limb, strength increased +16.4%

These effects were seen in all four types of contractions (isometric, concentric, eccentric and isotonic-dynamic) studied. Eccentric unilateral exercise seemed to provide the most cross-education effect, with the unused limb showing an average increase in strength of 17.7%.

So, what does this mean for your training? For one, it means that an injured limb could conceivably still be strengthened by performing unilateral exercises on the other side of the body. When performed correctly, this could help prevent atrophy in the injured limb and potentially limit the amount of imbalance between the two limbs that will exist when the injury heals. It also proves that the benefits of unilateral exercises go far beyond the limb that's being actively "trained," which further proves this type of exercise translates well to sports performance.

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