TIA LOW
The Martlet (University of Victoria)

VICTORIA (CUP) — Stroke patients affected by decreased strength on one side of their body can do high-intensity strength training on their unaffected side to improve their mobility, according to new findings by University of Victoria researchers.

Discovered in the 1800s, the cross-education effect is the idea that strength-training a muscle group on one side of the body can strengthen the same muscle group on the other side. In a person without any neurological damage, the untrained side typically gains half the strength that the trained side gains.

At first, Paul Zehr, the director at the U of V Centre for Biomedical Research, didn’t believe the cross-education effect had any significant implications for strength training.

“If you asked, ‘Hey, do you have any ideas about how to get stronger? I want to get my arm stronger,’ and I said, ‘Okay, do all these elbow flexions, but just do it with one arm and your other arm will get half as strong’… you would wonder why you don’t just train both arms so you get 100 per cent strength gains on both sides, and I would agree that’s a better idea,” Zehr said.

But what if one side of your body is significantly weaker than the other side? This is the question that led Zehr to study the cross-education effect in his stroke rehabilitation research lab.

Zehr’s research objective was to find ways to help people walk better after a stroke — the loss of brain function due to interrupted blood flow or the rupture of blood vessels in the brain.

Zehr and fellow researcher Katie Dragert, a U of V PhD student, recruited 24 stroke survivors to complete six weeks of training on their unaffected lower legs. Training involved “basically a piece of wood with a right angle on it and some straps that you can just put on the floor under your chair,” Zehr said. The participants would then “pull your toes up [using your] ankle… like you’ve got your foot in a ski boot.”

Results revealed equal improvement in the strength of both legs. At the end of the training period both participants’ legs were about 30 per cent stronger.

The results were “very strange but really exciting,” Zehr said. He expected the cross-education effect to be less prevalent in people who had suffered strokes than it was in people who had no neurological damage. He didn’t expect it to be more prevalent.

“Our wildest expectation was that it would be a smaller version of the effect we see in people who don’t have damage [to the nervous system], in terms of per cent changes. In fact, it was almost equivalent,” he said. “Not only did the cross-education effect work after a stroke; it works better.”

Zehr says cross-education is a result of small changes happening in many places throughout the body, including the spinal cord, reflex pathways that support the ability to contract muscles and parts of the brain that plan movement.

The sharing of information between the two halves of the brain also plays an important role. Many people believe the left side of the brain controls the right side of the body, and vice versa. But this is not completely true, Zehr said, who uses the example of flicking fingers on your right hand to illustrate.

“At the same time when the left side of your brain is active to move the right fingers, it is sending a message within your brain from the left side to the right side of your brain — which would control your left fingers — saying, ‘By the way, this is what [the right side of the body is] doing.’ ”

He said that information sharing between the right and left sides of the brain might be behind cross-education.

How or why this small change is amplified in stroke patients is unknown, but Zehr suggests two possibilities. First, people who have suffered a stroke end up in a weakened state that might allow their bodies to show more change when training. Second, a stroke could reveal connections between all limbs and the sides of the body that are partially hidden when the body is in a healthy state.

“It’s only when you’re in that damaged state that the phenomenon is really useful for recovery,” Zehr said.

Next, Zehr hopes to find out if this phenomenon works in the upper limbs as well. He predicts that, in the future, cross-education strength training will be one part of a bigger rehabilitation program for stroke patients in his lab.

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Graphic: Stephanie Mah