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Exercising One Arm Can Build Muscle in the Other, Study Shows

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Key Takeaways

  • Researchers found that some types of exercises performed by one arm can help to build strength in the other arm, even if it’s immobilized, for instance after injury.
  • The study findings could offer a solution to muscle wastage and loss of strength people often experience in an immobilized arm. 

The benefits of exercise are well-documented. But did you know that you could improve strength and decrease muscle loss in your arm without even moving it?

A recent study, published in The Scandinavian Journal of Medicine & Science in Sports, found that certain types of exercises performed by one arm can help build muscle in the other arm, even if it’s immobilized. 

What the Study Found

Each of the 30 participants had one arm immobilized for at least eight hours a day, for four weeks. They were split into three groups and asked to follow a set exercise regimen: one group did no exercise at all, one did a combination of eccentric and concentric exercises and the other performed eccentric exercise only. 

CJ Hammond, CPT

The majority of eccentric exercises help to improve range of motion, which equals an improved state of performance, helps to prevent dysfunctional patterns, and allows the body to protect the joints throughout daily activity.

— CJ Hammond, CPT

The researchers found that the group who used their active arm to do eccentric exercise only showed an increase in strength and a decrease in muscle atrophy (wastage) in their immobilized arm, which they labeled a “cross-transfer effect.” This group experienced only 2% muscle wastage in their immobilized arm, compared with the 28% loss of muscle in those who did no exercise at all. 

What’s the Difference Between Eccentric and Concentric Exercise? 

You might not be familiar with these specific terms, but if you’ve ever lifted weights, you’ve probably done plenty of both. In fact, every strength-training exercise (be it bodyweight or heavy lifting) can be split into three main elements: the concentric part, the eccentric part, and the isometric part. The concentric part happens when the muscle contracts, the eccentric part occurs when the muscle lengthens, and the isometric part happens when there’s no movement at all. 

CJ Hammond, CPT, trainer for RSP Nutrition and owner of sports performance gym Fit Legend, explains further. “An eccentric exercise is where the muscles are loaded under a lengthened state of tension,” he says. “The majority of eccentric exercises help to improve range of motion, which equals an improved state of performance, helps to prevent dysfunctional patterns, and allows the body to protect the joints throughout daily activity.”

A concentric exercise is the opposite. “Muscles are loaded at a shortened state, which helps improve muscle size,” says Hammond. “Concentric exercises maintain tension, or increase tension from a lengthened state to a shortened position.”  

Examples of Eccentric Exercises: 

  • A deadlift with focus on strengthening the hamstring on the downward position. 
  • The downward motion of a push-up, which allows the pectoral muscles to lengthen throughout this range of movement. 
  • The downward movement in a squat when the hips come closer to the ground, which works the quad muscles. 
  • Bringing the shoulders closer to the bar during dips lengthens the triceps, which create an eccentric movement.

Examples of Concentric Exercises:

  • Cable tricep extension, when pushing the cable down and shortening the tricep, is an example of concentric tension on the bicep.
  • Any type of bicep curl when bringing the barbell or cable to a raised position, with the biceps shortened. 
  • The most simple comparison of eccentric vs. concentric exercise is walking downstairs (eccentric) vs. walking upstairs (concentric). 

Luis Penailillo

If you can’t produce movement or muscle contractions in an injured limb, it’s possible that the training of the non-injured limb will maintain or even increase the muscle strength in the injured limb.

— Luis Penailillo

A New (Better?) Approach to Rehab 

One of the study authors, Luis Penailillo, from the Exercise Science Laboratory at the Universidad Finis Terrae’s School of Kinesiology in Santiago, Chile, says that the findings challenge conventional rehabilitation methods for an injured limb, such as rest or cast (immobilization). 

“If you can’t produce movement or muscle contractions in an injured limb, it’s possible that the training of the non-injured limb will maintain or even increase the muscle strength in the injured limb,” he says. So it’s possible that exercising the other side of the body with high-intensity eccentric exercises may accelerate a return to activity or sport. 

The researchers hope their research can be expanded upon in the future. To figure out if this type of training (known as contralateral training) is well-tolerated and safe for patients or athletes during recovery from acute injury or surgery, Penailillo says it will be necessary to carry out evaluations in specific clinical setups (i.e. on real injuries with immobilizations).  

What This Means For You

If you're trying to maintain strength and muscle when recovering from a limb injury, take advice from your primary care provider, physiotherapist and personal trainer.

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  1. Valdes O, Ramirez C, Perez F, Garcia-Vicencio S, Nosaka K, Penailillo L. Contralateral effects of eccentric resistance training on immobilized arm [published online ahead of print, 2020 Sep 8]Scand J Med Sci Sports. 2020;10.1111/sms.13821. doi:10.1111/sms.13821