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1st Mar

2014

Crossover Strength Training in Physical Therapy

The topic of this month’s newsletter is crossover training, also referred to as cross-education strength training, or motor overflow. It refers to the mechanism by which strength training of one limb automatically results in increase in strength of the same muscle in the opposite limb which was not exercised. Studies have shown that such strength gain can be close to 20%. The higher intensity strength training used, the greater than effort typically is.

Studies have also shown that immobilization due to injury or surgery causes rather rapid loss of strength and muscle thickness (around 20% after only three weeks). Using crossover training during such immobilization, recent research have shown that we can essentially maintain normal muscle strength and thickness in the immobilized muscles, at least during the first three weeks. Therefore, especially for an athlete, using such training can be instrumental in recovering quicker and facilitating the whole rehabilitation process. In the last 3-5 years, new exciting research, using functional magnetic resonance imaging (fMRI), and transcranial magnetic stimulation (TMS) have confirmed that the crossover mechanism has a cortical or subcortical supraspinal origin, i.e. it lies in the brain. Crossover training has been shown to cause certain areas in the brain to light up on scans and something called corticospinal excitability for the untrained muscles has been shown to increase. The result is increased muscle activity in the limb which is not being exercised, measurable also with EMG.

Not only can such crossover training be effective when used with one limb immobilized, but it can be very effective once the arm or leg is allowed to be moved. It can then gently be moved against gravity without pain and with good coordination, while the opposite limb simultaneously performs the same motion with considerable resistance.

Further down the road, when the affected extremity can take light resistance, the same method can be used to allow quicker exercise progressions and gain of tissue strength and muscle qualities, while completely avoiding pain and allowing for a normal motion pattern to be learned. The end result is faster recovery of function and strength, and return to sports or normal daily activities.

We utilize this method quite a bit in our clinic. Although most high level athletes do the same, it is less known or practiced in many physical therapy clinics. Once you understand the principle, it is not difficult to incorporate such a method yourself into your training following injury, although it is always advisable to seek physical therapy help following surgery or injuries that don’t heal quickly by themselves.

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