If you've ever broken an arm or a leg, you know that when the cast finally comes off, your long-immobilized limb looks puny and doesn't have half the strength that it did pre-break. The reason for this is fairly obvious: When muscles don't get worked, they lose strength. But according to a new study, your brain also plays a role in muscle strength — both in gaining and losing it — and you may even be able to prevent a significant amount of strength loss with thoughts alone.
Researchers at the Ohio Musculoskeletal and Neurological Institute convinced 29 healthy volunteers to wear rigid elbow-to-finger casts for four weeks. Half of the group was told to do nothing, while the others were instructed to imagine they were contracting their immobilized wrist (as if they were pushing their hand really hard against a flat surface) for five seconds and then relaxing it for another five. These people weren't actually moving their wrists (they couldn't); they were simply imagining how it would feel if they were. They did this mental contract-relax regimen four times in a row, then rested for one minute. The volunteers repeated this sequence a total of 13 times per session, doing five sessions per week for four weeks straight.
When all of the participants' arms were freed from their casts after four weeks, everyone had lost strength in their wrist flexor muscle. However, the cast-wearers who did not do any mental exercises lost 45 percent of their strength, nearly double the group that imagined moving their wrists. Additionally, those who performed the mental exercises also regained voluntary activation — the nervous system's ability to fully activate the muscle — more quickly than the other group.
"The nervous system controls muscles, so imagery helps maintain neural pathways and remember how to do a task effectively," says lead researcher Brian Clark. "Basically, imagery helps the brain remember how to activate the muscles. We see this all the time when people are learning a task, such as swinging baseball bat. They're usually not very good at it at first, but then they get progressively better." That improvement, he says, stems in part from the muscles getting physically stronger, but also because the brain and muscles have fallen into sync, and the muscles have essentially remembered how to properly swing the bat so that it connects with the ball.
Clark says many sports psychologists are already helping injured professional and college athletes to use mental imagery to attenuate strength loss. But before his study, no previous research had demonstrated just how effective this tactic could be.
He believes mental imagery should work to preserve strength in most any out-of-commission muscle, but it's important that you do it correctly. "There are different types of imagery," Clark says. "The differences are subtle, but they make a big difference in terms of which part of the brain is activated. What we're talking about here is not creating a picture of yourself doing the contracting and relaxing and then watching yourself from a third-person perspective. Rather, you must actually urge your body to perform these motions, without actually doing them, and try to feel what they would feel like. We had our volunteers practice these motions before their arms were put into casts, so one they were immobilized, their muscles would know what to do."
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