The cross-education effect or phenomenon is when strength/resistance training performed on
one side of the body produces strength gains not only on that side but also on the opposite side
of the body. Yes, you read that right! You can actually get stronger, to an extent, without directly
working out those muscles. In other words, say you were to complete a strengthening workout
regimen only on your left arm…your left arm should definitely get stronger, but your right arm
may develop some relative increased strength as well!
How does it work?
Although the cross-education effect is not completely understood, there has been some
research showing possible mechanisms. The most researched and proven mechanism as of
today is due to the changes that are made in the nervous system from performing exercises.
Neurological adaptations are made from our mind-to-body connection that we have through our
nerves when we activate our muscles, even to the side that we are not using.  Another possible
mechanism may be through the body’s endocrine response to exercise by sending specific
signals through our body’s hormones to stop muscle breakdown in the opposite unused limb. 
Types of training that increase the cross-education effect:

  1. Externally paced training with the use of a metronome
    a. Increases the cognitive aspect aka more neuroplasticity or neurological
  2. Eccentric or negative muscle contractions have shown possible increases in the cross-
    education effect, but more research is needed. 
    a. Nonetheless, eccentric training is important to include in strength training
    regardless…so might as well incorporate it!
    Who would benefit the most from the cross-education effect?
    The cross-education effect can be very useful during times when strength training is not allowed
    due to injury and/or surgery, intolerable due to pain, or a combination of all three. Also, when a
    person has an injury and/or surgery the affected limb may be immobilized in a brace or sling.
    When this happens, you are unable to use that limb like you normally would…so you’re not
    using your muscles normally. This immobilization is necessary to allow for proper healing of the
    tissue but unfortunately causes muscle wasting. Utilizing the cross-education effect can help
    counteract the muscle wasting and allow for a faster/easier recovery once you are cleared to
    start strengthening the affected limb.

-Dr. Arron Pierce PT, DPT

-Hendy, Ashlee & Lamon, Séverine. (2017). The Cross-Education Phenomenon: Brain and Beyond. Frontiers in Physiology.