Can you improve the health of one part of the body by exercising a different part of it? As unlikely as it sounds, the idea is gaining traction among scientists looking for new ways to deal with the effects of chronic disease, stroke and even breast cancer surgery.
Now researchers at the University of Texas at El Paso, in the US, are about to test a remarkable new theory that it is possible for people with osteoarthritis to eliminate knee pain by exercising their arms.
Last week, researchers launched a new clinical trial where 60 men and women who experience frequent pain from wear and tear in their knees will try different exercises to see which provides the most relief.
The trial, due to end in 2025, will test whether regular 20-minute arm exercise (using an ‘arm cycle’ machine, such as those found in gyms) is better than leg cycling for relieving knee pain and increasing mobility.
The aim is to try to replicate the findings of previous small studies suggesting that hand cycling is better than treadmill walking for knee pain relief.
Researchers have launched a new clinical trial where 60 men and women who experience frequent pain from wear and tear in their knees will try different exercises to see which provides the most relief (stock image)
Regular, moderate exercise is one of the best ways to manage arthritic knee pain because it strengthens the muscles around the joint and takes pressure off the damaged area.
But walking or jogging can increase the load on the knee, making it difficult for some to move. “There is no obvious mechanism by which arm exercises are likely to target knee pain,” says Uzo Ehiogu, consultant physiotherapist at Birmingham Royal Orthopedic Hospital, when commenting on this approach.
“What probably happens is that patients feel better and more confident and can be more mobile, after 20 minutes of arm exercise, which can then reduce the feeling of pain in their knees.”
But in some cases, exercising one limb does have a direct and fascinating effect on the opposite.
The most recent proof of this came in a study published in July in the Scandinavian Journal of Medicine and Science in Sports.
Researchers from the National Taiwan Normal University in Taipei, Taiwan, recruited 30 volunteers who held one arm completely still for hours at a time while flexing the muscles of the free arm; others kept both hands still.
After a few weeks, those who contracted the muscles in the moving arm lost only 2 percent of the muscle in their stationary arm.
However, in the no-exercise group, muscle loss in the static arm was 28 percent.
This effect is known as muscle cross-training, where muscles on one side of the body benefit from the activity of those on the other side. It is routinely used in sports medicine to reduce rapid muscle wasting during injury.
Research shows that an injured arm in a sling loses up to 60 percent of its muscle strength in the first five weeks. “But by regularly exercising the other limb ‘contralaterally’ the muscle wasting will be greatly reduced,” says Mr Ehiogu.
It is not clear exactly how muscle cross-training works. One theory is that it’s a “spillover” effect, whereby giving the good limb a thorough workout (by lifting weights with one arm or doing single-leg squats, for example) also generates new connections between the brain and the injured limb.
After several weeks, those who contracted the muscles in their mobile arm lost only 2 percent of the muscle in their stationary arm (stock image)
But the key to its success, says Mr Ehiogu, who is a spokesman for the Chartered Physiotherapy Society, is to work the good limb harder than you normally do by increasing the resistance, ie. lifting more weight.
“You should be working at 80 to 85 percent of your maximum capacity,” he says. “So if you normally manage ten reps at 50 percent of your max, aim to do five reps instead, but at 80 or 85 percent of your capacity.”
“If you don’t increase the resistance, you won’t get the crossover effect.”
One of the most intriguing examples of this phenomenon is mirror therapy, which is used in stroke patients paralyzed on one side.
Their damaged arm is placed in a box with a mirror on the outside; the patient then does a series of exercises with the good hand to improve strength and grip while looking at the same hand in the mirror.
This “tricks” the brain into thinking that it is working on the damaged arm, stimulating connections with the nerves and muscle fibers in it.
Walking or jogging can increase the load on the knee, making it difficult for some to move (stock image)
A 2018 Cochrane review of mirror therapy in stroke care (which examines the evidence for medical treatments in detail) concluded that it improves movement of paralyzed limbs enough for patients to carry out daily activities such as cleaning.
And a study in the Journal of Cancer Survivorship in June, from Fudan University in China, found that mirror therapy also helped women with limited shoulder function after surgery or radiotherapy for breast cancer.
Both treatments can lead to immobility and pain as a result of tissue removal, nerve damage and scarring. In the study, half of the 79 participants exercised their unaffected arm daily while looking at it in a mirror; the rest did the same without a mirror.
After eight weeks, the mirror group had better range of motion in the affected arm than their peers. In a report on the findings, the researchers said: “Breast cancer survivors can try mirror therapy for effective shoulder rehabilitation.”
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