When an injury or an illness stops you from moving a limb, you’ll lose muscle strength and mass quickly.
But there are ways to keep your muscle strength up: including, weirdly, exercising the other limb.
Called the “cross-education effect”, it’s where exercise on one side of the body builds muscles on the other side.
A study published in Medicine and Science in Sports and Exercise has found one type of exercise that’s best for this – at least if you’re wearing a cast over your elbow.
The team of Australian and Taiwanese researchers showed that “eccentric” training (exercises that lengthen the muscle, like lowering a weight) is the most effective cross-education trick.
Lead researcher Professor Ken Nosaka, from Edith Cowan University, says that it’s well-known among researchers and some physiotherapists that exercising one limb will enhance the muscles on the opposite limb.
“About 50% of the training effect is transferred to the other arm or other leg – for example, if you can increase the strength of one of the arms by 20%, you can increase the strength for the non-trained arm by 10% or so,” says Nosaka.
“However, in this particular study, we found that if we are doing eccentric training – in this case, lowering a dumbbell slowly – then the cross-education is much, much greater.
“We found no strength loss. Strength even increased a little bit, and also there was no hypertrophy at all.”
The researchers asked 36 volunteers, all sedentary young men, to wear a cast on their elbow joint for three weeks.
“This is a very demanding kind of condition, because they cannot use one of their arms,” says Nosaka.
That said, he adds that the exercise that subjects had to do wasn’t as time-consuming as other similar studies.
Participants were then sorted into three groups of 12: one control group did no exercise, one group did concentric exercises (lifting a dumbbell) twice a week, and one group did eccentric exercises (lowering a dumbbell) twice a week.
When the casts came off, the control group had unsurprisingly lost strength in their immobilised arm: a decrease of about 15%.
The concentric exercise group saw only a 4% loss in strength in their immobilised arm.
And the eccentric group had increased their strength in their immobilised arm: they were 4% stronger on average.
Nosaka says that, because the study was done on men with an average age of 23, they don’t know whether the results would be the same in women, or older or younger people.
“But I assume so. In this area, there’s not so much difference between age groups, and also the sex difference is very minor.”
He adds that cross-education training – and particularly eccentric training – should become more common for people recovering from injuries.
“Not many people are doing even cross-education training for an immobilised arm or immobilised leg condition, but they should be doing more,” says Nosaka.