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Tip 221:Perform Single-Side Training When Injured and Stay Strong in Both Limbs: Cross-Education Principle

Wednesday, November 23, 2011 7:02 AM

If you’re injured, perform single-side training in the non-injured limb and you will minimize the effects of detraining. It’s well established that if you suffer an injury that causes you to be out of commission on one side, you can maintain strength and accelerate healing by training the uninjured limb. For example, if you dislocate your right shoulder and can’t train with your right arm for three weeks, by performing exercises with the left arm, you can decrease strength loss and speed recovery due to an effect known as “cross-education.”

Cross-education occurs when you strength train a limb on one side of the body, which results in an increase in strength in the same limb on the other side of the body due to neural adaptations. It doesn’t just work arms and legs, but cross-education appears to be effective for all muscles including those around the ankle and wrist joints. The cross-education effect is more pronounced when the non-dominant limb is immobilized and the dominant limb is doing the work, but there is evidence it works in the opposite case as well.

A review of previous studies testing the cross-education effect in the Journal of Exercise Science and Fitness showed that strength gains in the untrained limb are typically in the range of 5 to 25 percent depending on if that limb is dominant or not. Strength gains average around 35 and 60 percent of those in the trained limb. In studies that included a control group, strength gains in the untrained limb averaged about 8 percent, while not immediately impressive, these gains are certainly better than strength loss due to immobilization. Additionally, it appears that less range of motion will be lost in the injured limb due to the cross-education effect—a major benefit for athletes and trainees.

New research in the Scandinavian Journal of Medicine and Science in Sports calls attention to this fascinating strength transfer effect and shows that cross-education works on muscles besides the contralateral homologous muscle groups. This means that if you have an injury in the left wrist and train using right wrist flexion exercises but not extension, you can increase strength in the left wrist extensors (untrained motion) as well as the flexors(trained motion). Strength can be gained in the agonist and antagonist muscles in the contralateral untrained limb.

This study used electrostimulation of the right wrist flexors using an eccentric contraction and demonstrated impressive strength gains in the untrained wrist muscles. Participants received the electrostimulation five days a week for six weeks. The untrained left wrist extensor and flexor muscles increased strength significantly, both improving by about 45 percent. Researchers suggest that strength gains in the immobilized limb were substantial because eccentric contractions were induced by using electrostimulation that triggered a maximal voluntary contraction in the right wrist, thereby providing greater neuromuscular stimulus to than a concentric contraction.
  
Cross-education is not completely understood, but strength gains in the injured limb are likely from neuromuscular adaptations and increased neural drive to the untrained muscle. A related hypothesis is improved motor control  because training the healthy limb results in recruitment of more high-threshold motor units in both limbs. There is no evidence of hypertrophy or changes in muscle fiber types in the immobilized muscle following single-side training. 

Cross-education highlights the importance of single-side training cycles because it will provide variation to your program and correct structural imbalances.  Plus, it’s a valuable but lesser known tool in the case of injury or immobilization. Clients or athletes should be easily persuaded to continue single limb training during injury once they become aware of the impressive gains in strength despite being injured, and continuing to train will likely speed recovery. Cross-education of strength is a perfect example of how you can turn a weakness into a strength—literally.

Take note that even though single limb training is an excellent tool when injured or to address structural imbalances, you  still have to train bilaterally to trigger hypertrophy and an anabolic response.  To read more about the use of single-side training, check out the tip Strategic Programming—Use Unilateral Lifts After Large Muscle Group Lifts for Optimal Anabolic Response.
 

References:
Sariyildiz, M., Karacan, I., et al. Cross-Education of Muscle Strength: Cross-Training Effects are not Confined to Untrained Contralateral Homologous Muscle. Scandinavian Journal of Medicine and Science in Sport. April 2011. Published Ahead of Print.

Lee, M., Carroll, T. Cross-Education: Possible Mechanisms for the Contralateral Effects of Unilateral Resistance Training. Sports Medicine. 2007. 37(1), 1-14.

Zhou, Shi. Cross-Education and Neuromuscular Adaptations During Early Stage of Strength Training. Journal of Exercise Science and Fitness. 2003. 1(1), 54-60.
 

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