Can you improve the health of one part of the body by training another part of it? As unlikely as it sounds, the idea is gaining traction among scientists looking for new ways to manage the effects of chronic diseases, strokes and even breast cancer surgery.
Now researchers from the University of Texas at El Paso, in the US, are about to test a remarkable new theory that it could be possible for people with osteoarthritis to drive away the pain in their knees – by stretching their arms. to practice.
Last week, researchers launched a new clinical trial in which 60 men and women who regularly experience pain due to wear and tear on their knees will try different exercises to see which provides the most relief.
The trial, due to be completed in 2025, will test whether regular 20-minute arm exercises (using an ‘arm cycle’ machine such as those found in gyms) are better than leg cycling for relieving knee pain and increasing mobility.
The goal is to replicate findings from previous small studies that suggested that arm cycling is better than treadmill walking for relieving knee pain.
Researchers launched a new clinical trial where 60 men and women who regularly experience pain due to wear and tear on 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 treat arthritic knee pain because it strengthens the muscles around the joint and takes pressure off the damaged area.
But walking or jogging can increase stress on the knee, making it difficult for some to get moving. ‘There is no obvious mechanism by which arm exercise is likely to address knee pain,’ says Uzo Ehiogu, a physiotherapist at the Royal Orthopedic Hospital in Birmingham, commenting on this approach.
‘What is likely to happen is that patients feel fitter and more confident, and possibly more mobile, after a 20-minute arm workout, which can then reduce the feeling of pain in the knees.’
But in some cases, training one limb really does have a direct – and fascinating – impact on the other.
Recent evidence for this came from a study published in July in the Scandinavian Journal of Medicine and Science in Sports.
Researchers from National Taiwan Normal University in Taipei, Taiwan, recruited 30 volunteers who held one arm completely still for hours while flexing the muscles in their free arm; others kept both arms still.
After several weeks, those who contracted muscles in the mobile arm lost only 2 percent of the muscle in their immobile arm.
However, in the motion-free group, muscle loss in the static arm was 28 percent.
This effect is known as muscle cross-education, 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 loss during injuries.
Research shows that an injured arm in a sling loses up to 60 percent of its muscle strength in the first five weeks. ‘But with regular exercise of the opposite limb – ‘contralateral’ training – muscle wasting will be significantly reduced,’ says Mr Ehiogu.
It is not clear exactly how muscle cross-education works. One theory is that there is a ‘spillover’ effect, whereby giving the good limb thorough training (for example, lifting weights with the arm or doing squats on one leg) also generates new connections between the brain and the injured limb.
After several weeks, those who contracted muscles in the mobile arm lost only 2 percent of the muscle in their immobile arm (stock image)
But the key to success, says Mr Ehiogu, spokesman for the Chartered Society of Physiotherapy, is to train the good limb harder than you normally would by increasing resistance – that is, by lifting a heavier weight.
“You need to be operating at 80 to 85 percent of your maximum capacity,” he says. ‘So if you can normally do ten reps at 50 percent of your maximum, try doing five reps instead, but at 80 or 85 percent of your capacity.
‘If you don’t increase the resistance, you don’t get a crossover effect.’
One of the most intriguing examples of this phenomenon is mirror therapy, which is used in stroke patients who are 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 arm to improve strength and grip – while looking at the same arm in the mirror.
This ‘tricks’ the brain into thinking it is working on the damaged arm, creating connections to the nerves and muscle fibers within it.
Walking or jogging can increase stress on the knee, making it difficult for some to get moving (stock image)
A 2018 review of mirror therapy in stroke care by Cochrane (which examines the evidence for medical treatments) concluded that it improved movement of paralyzed limbs enough for patients to perform daily activities such as cleaning.
And a study in the June Journal of Cancer Survivorship by Fudan University in China found that mirror therapy also helps women with limited shoulder function after surgery or radiation therapy for breast cancer.
Both treatments can lead to immobility and pain due to tissue removal, nerve damage and scarring. In the study, half of the 79 participants exercised their sound 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, researchers said: ‘Breast cancer survivors can try mirror therapy for effective shoulder rehabilitation.’