How doing ARM exercises could ease KNEE pain

Can you boost the health of one part of the body by exercising a different part of it? As unlikely as it sounds, the idea is gaining ground among scientists looking for new ways to manage the effects of chronic illness, stroke and even breast cancer surgery.

Now researchers at the University of Texas at El Paso, in the U.S., are about to test a remarkable new theory that it may be possible for people with osteoarthritis to banish the pain in their knees — by exercising their arms.

Last week, the researchers launched a new clinical trial where 60 men and women who experience frequent pain as a result of wear and tear in their knees will try out different exercises to see which provides the most relief.

The trial, due to finish in 2025, will test whether regular 20-minute bouts of arm exercise (using an ‘arm cycle’ machine such as those found in gyms) is better than leg cycling for easing knee pain and increasing mobility.

The aim is to try to replicate findings from previous small studies that suggested arm cycling is better than walking on a treadmill at soothing knee pain.

Regular, moderate exercise is one of the best ways to manage arthritic knee pain, as it strengthens muscles around the joint and takes pressure off the damaged area.

But walking or jogging can increase the load on the knee, so it is difficult for some to get moving. ‘There’s no obvious mechanism by which exercising the arms is likely to target pain in the knees,’ says Uzo Ehiogu, a consultant physiotherapist at the Royal Orthopaedic Hospital in Birmingham, when commenting on this approach.

‘What’s probably happening is patients feel fitter and more confident, and may be more mobile, after a 20-minute arm workout, which may then reduce the sensation of pain in the knees.’

But, in some cases, working out one limb really does have a direct — and fascinating — impact on the opposite one.

Recent evidence for 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 kept one arm completely still for hours at a time 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 just 2 per cent of the muscle in their immobile arm.

However, in the exercise-free group, muscle wastage in the static arm was 28 per cent.

This effect is known as muscle cross education, where muscles on one side of the body benefit from activity in those on the other side. It is routinely used in sports medicine to reduce rapid muscle loss during injury.

Studies show an injured arm in a sling loses up to 60 per cent of its muscle strength in the first five weeks. ‘But with regular exercise of the other limb — ‘contralateral’ training — muscle wastage will be much reduced,’ says Mr Ehiogu.

It’s not clear precisely how muscle cross education works. One theory is it’s a ‘spillover’ effect, whereby giving the good limb a thorough workout (by lifting weights with the arm or doing squats on one leg, for instance) also generates new connections between the brain and the injured limb.

But the key to its success, says Mr Ehiogu, who is a spokesperson for the Chartered Society of Physiotherapy, is to work the good limb harder than you usually would by increasing resistance — i.e. lifting a heavier weight.

‘You need to be working at 80 to 85 per cent of your maximum capability,’ he says. ‘So if you normally manage ten repetitions working at 50 per cent of your maximum, aim to do five reps instead but at 80 or 85 per cent of your capacity.

‘If you don’t increase the resistance, you don’t get the crossover effect.’

One of the most intriguing examples of this phenomenon is mirror therapy, used in stroke patients paralysed on one side.

Their damaged arm is placed inside 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 watching the same arm in the mirror.

This ‘tricks’ the brain into thinking it’s working the damaged arm, firing up connections with the nerves and muscle fibres in it.

A 2018 review of mirror therapy in stroke care by Cochrane (which scrutinises evidence for medical treatments) concluded it improved movement in paralysed limbs enough for patients to carry out daily activities such as cleaning.

And a study in the Journal of Cancer Survivorship in June, by Fudan University in China, found that mirror therapy also helps women with limited shoulder function after surgery or radiotherapy for breast cancer.

Both treatments can lead to immobility and pain as a result of the removal of tissue, damage to nerves and scarring. In the study, half of the 79 participants exercised their non-affected 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 movement 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.’