One of the most common questions we hear in our Boulder Physical Therapy and Lafayette Physical Therapy clinics is should I exercise my non involved side. As they enter Physical Therapy to recover from a single sided (ex. right arm) injury or surgery they are asking if there are additional benefits of exercising their opposite or uninvolved side (ex. left arm). There is always a benefit of exercising the uninvolved side for its’ own benefit (mobility or strength), but research has documented benefits on the involved side as well.

The cross over effect describes the benefits on a given side of the body when the opposite side is exercised. As strange as it is to believe, exercising one side of our body has been shown to improve balance, flexibility, strength, and power of the opposite side that did not perform any exercise. Researchers believe this is primarily mediated by neurological changes in the central and peripheral nervous systems. Its’ impact is most important when we considered individuals who are unable to exercise a side of their body due to injury, surgery, or immobilization in a brace or cast.

A recent research study was conducted to determine the impact of exercising the opposite limb among individuals who were immobilized in their opposite extremity (Chen et al. Med Sci Sp Ex. 2023). Authors immobilized the non dominant elbow of 12 healthy participants for 3 weeks after they underwent pre immobilization testing of both arms including strength and muscle size. Participants were then randomized to either perform 5 sets of 6 reps, twice a week, of eccentric or concentric bicep curls at up to 80% of their 1 rep max. Some participants assigned to the control group did not perform any exercise. All participants completed the post immobilization measurements at the end of the 3 weeks. As expected measurements were improved on the trained side after the short 3 week exercise period. Interestingly, the immobilized side also showed improved strength and less atrophy (muscle loss) compared to participants in the control group. Of the two exercise types, eccentric training showed greater improvements in these outcome measures.