When you injure an arm, exercising the same healthy limb on the other side of the body may be key to maintaining strength and muscle size in the injured limb, a University of Saskatchewan study shows.
“We hope strength-training of the healthy limb may one day be included in standard of practice for recovery,” said kinesiology PhD student Justin Andrushko, who did the study with supervisor Jonathan Farthing. “But first we need more research to study the effects and causes of the phenomenon.”
Andrushko’s preliminary research has just been published in the Journal of Applied Physiology. “Cross-education” effects from single-arm exercise have been known since the 19th century but researchers don’t know exactly why it occurs.
Andrushko and Farthing recruited 16 U of S students for their study, and asked them to wear casts that immobilized their wrists for a month. Half of the students did wrist-flexion training on their non-casted arm, and half did not, so that the researchers could compare changes in muscle strength and size in the immobilized wrists.
Andrushko found that students who did the training preserved the strength of their wrist muscles in the casted arm, while in the non-exercising group the strength of wrist muscles decreased by 20 per cent. He said strength preservation was localized only to the wrist flexor muscles of the casted arm, and not the extensors.
“The strength preservation likely comes from a phenomenon related to how exercising one side of the body affects information exchange between the two sides the brain, and then influences the non-trained side of the body,” said Andrushko. This information exchange is well known from previous research, some of it by Farthing.
The students who did the “cross-education” training also preserved their muscle size, not just strength, compared to those who didn’t. Andrushko found the non-exercising group lost on average three per cent of muscle.
He is the first to study muscle size preservation by using a peripheral Quantitative Computed Tomography (pQCT) scanning, which offered a more in-depth picture of the entire forearm, unlike previous ultrasound-based studies.
The cause behind muscle size preservation is still a mystery, but the researchers think exercising may trigger a yet-unknown connection between the nervous system and a protein balance mechanism that helps maintain muscle size.
“We do not know much about the causes of muscle size preservation, so we need to dig deeper,” said Farthing. “This was an initial study on healthy, young people. There may be unknown factors at play when applying this to injured people, and the results could change.”
While this study was Andrushko’s master’s project, he is now working with Farthing to study the effects of “cross-education” on stroke patients. Because strokes often cause serious loss of muscular strength on one side of the body, Andrushko is interested to see how exercising the less affected side could benefit rehabilitation.
Farthing’s projects are funded by the federal agency NSERC, the Saskatchewan Health Research Foundation (SHRF) and the Royal University Hospital Foundation. Andrushko’s master’s project was also funded by the Canadian Institutes of Health Research (CIHR).
Federica Giannelli is a graduate student intern in the U of S research profile and impact unit.
This article first ran as part of the 2018 Young Innovators series, an initiative of the U of S Research Profile and Impact office in partnership with the Saskatoon StarPhoenix.