Brain to brawn: Training one leg strengthens both after stroke

To recover strength and ultimately perhaps the ability to walk, the best bet after a severe stroke might just be to forego working the weaker, more-affected side. It seems counter-intuitive, but high-intensity strength training on the less-affected side could have remarkable potential for helping recover mobility after a stroke, new UVic research indicates.

The notion of cross-education of strength—training one side of the body achieves strength gains in the corresponding muscles on the other side—has had considerable study since it was first proven at Yale University in 1894. Typically, the corresponding strength gain in the non-trained side is about half the improvement on the trained side.

While an interesting phenomenon, it’s not had serious clinical application, since most people or patients are looking to strengthen both sides of their body symmetrically.

“It just sat in the literature as one of those quirky observations,” says Dr. E. Paul Zehr, professor of neuroscience in the Division of Medical Sciences and School of Exercise Science, Physical and Health Education at UVic.

But Zehr, who studies how the arms and legs work together while we walk and how that information can be used to help recover walking when it’s been lost due to nervous system damage, thought cross-education might be useful for people with an existing asymmetry, such as those who’ve suffered a stroke.

“After a stroke, you’re weaker all over, but it’s more prominent on one side,” says Zehr. “The standard way to recover walking is to strength-train that weak side, particularly the leg.”

A couple years ago, Zehr started thinking about “tapping into” the weaker side indirectly by using the less-affected limb and decided the idea needed to be explored.

And his study showed remarkable results. Training on the less-affected side of the body in post-stroke patients achieved equivalent strength gains (about 30 per cent) on both sides. The researchers had predicted about a 5–10-per-cent strength gain.

“I never imagined that it would come out like this,” says Zehr. “The results exceeded any normal expectations.”
The results of the study, the first time the theory was tested for stroke sufferers, are to be published in the journal Experimental Brain Research and are already online.

Zehr notes that the results show huge potential for neurological rehabilitation because the strength gain was equal on both sides, but also because the training effect was shown well after a stroke event. Of 19 study participants, many were years after a stroke event and the average was 80 months after a stroke.

“It doesn’t matter how long it’s been after a stroke, strength can still be recovered,” says Zehr.

Study participants completed six weeks of training, involving three sessions a week—two at home and one in the lab, without aid of any specialized equipment.

The study focused on the legs with an eye toward walking recovery. Zehr says the next steps are to test cross-education of strength in the upper body “to come at the more affected leg from different angles” and work toward integrating the practice into a full walking retraining program.

“The big-picture view is looking at changing the way we do mobility rehabilitation,” Zehr says.