By Caitlin, Sports Rehab Therapist
In 1899, a researcher called Walter W. Davis discovered the phenomenon of limb cross-education; otherwise known as contralateral learning, inter-limb transfer, cross-over effect and cross-exercise (wow, that’s a mouthful!).
But simply It refers to the increase in strength seen in an immobile/untrained limb following training of the opposite limb.
Why is this important in rehabilitation?
Lots of things can lead to a period of decreased mechanical loading of your legs, and subsequent deconditioning of the muscles. For example, you may be required to wear a cast for 6 weeks following a leg fracture. A study showed that even 5 days of leg immobilisation in a cast can lead to a 3.5% lossin quadricep muscle cross-sectional area and a 9% lossin overall strength. This rate is even more significant after the age of 30, where muscle mass starts to decrease at a faster rate. Gulp!
The reason this occurs in an immobile limb is due to decreased neural drive (activation) to and from the brain to these muscles.
Neuromuscular electrical stimulation using a TENS machine has been found to prevent muscle atrophy (wastage) during leg immobilisation. This principle explains how cross-education may work; mobilisation of the good limb improves neural activity in both sides of the primary motor cortex (the brain region that plans and executes movement). Therefore, rehabilitating the good limb could potentially minimise the amount of deconditioning of the injured side.
So what type of exercises do you need to do this?
Resistance exercise has long been proven to elicit the fastest strength changes in muscle. Research has compared different variables in resistance exercise (concentric and eccentric training, exercising to fatigue, number of repetitions and sets) and their effect on strength, cross-sectional area, force production and electrical activation (i.e. muscle conditioning).
Although evidence continues to question cross-education, eccentric training of the good limb has had the most positive effect on strength and neural activity of the injured limb; by increasing acute and long-term excitability and activity of the brain. This transference during unilateral tasks has also been shown to help those suffering from phantom limb pain (a fascinating concept where patients with amputated limbs feel pain in the part of the limb no longer there).
Research continues to develop on the subject, with scientists and rehabilitation specialists looking further into the use of cross-education training in slowing the rate of deterioration in muscle mass and strength during periods of immobilisation.
The exciting thing is that this concept helps our Physio Edge patients back to sport and activity quicker!
See you in clinic…