Injuries are zero fun, but the reality is, most of us are going to be sidelined at some point. An arm in a sling or a foot in a boot? UGH! Please, NO!!!
But hold up. If that happens, all is not lost. You can still train. AND you can actually do something to minimize strength loss - IN THE LIMB THAT’S IMMOBILIZED.
NEUROLOGICAL ADAPTATION
Cross education was first reported by the Yale Physiological Laboratory in 1894, so it's been around for quite a while. Cross education is a neurophysiological adaptation where an increase in strength is witnessed in an untrained limb following unilateral strength training in the opposite, contralateral limb.
In other words, if your right arm is in a sling, and you do biceps curls with your left arm, your right bicep will get stronger.
HOW MUCH STRONGER?
One meta-analysis revealed that the typical magnitude of strength gain in the untrained limb is 7.6% Another meta-analysis estimated a 7.8% increase.
However, a separate review of 141 unilateral training units yielded the following results:
- Strength gains of 18% in young adults
- Strength gains of 15% in older adults
- Strength increase of 29% in populations consisting of post stroke, neuromuscular disorders, and osteoarthritis patients.
One important thing to note: cross education results in an increase in muscle strength but NOT in muscle size.
HOW DOES IT WORK?
The cross-education effect is mainly explained by increased neural drive originating from the untrained motor cortex. However, most researchers agree that there’s probably more to it. Systemic and hormonal factors most likely make a major contribution, but at this point, there’s not enough research to say definitively.
WHAT’S IT GOOD FOR?
Ultimately, cross-education has the greatest application in two situations:
- When training through an acute injury or
- When training with a unilateral neurologic disorder such as stroke.
