Thursday, May 17, 2018

Exercising your left arm makes your right arm stronger

According to a fascinating new study, working out the muscles on one side of our bodies can keep the muscles on the other side strong and fit, even if we do not move them at all. ...

There have been hints... that exercising one limb can affect the other. In past studies, when someone pedals a bike with one leg or lifts weights with one arm, muscles in the other limb often contract, a development known as mirroring.

But in most of those experiments, the unused limb was not completely immobilized with a cast and scientists did not focus on specific muscles, making it difficult to know whether exercising certain muscles in one limb affects all muscles in the other or only some.

So for the new study, which was published in April in the Journal of Physiology, researchers from the University of Saskatchewan in Canada gathered 16 male and female college students and closely examined their wrists. ...

Then they covered each student’s left forearm and wrist with a hard cast to freeze the wrist in place. (All of the students were right-handed.)

Half of the students were then asked to go on with their normal lives, ignoring the cast as much as possible and not exercising their arms.

The other eight students, though, began a workout program that targeted the flexor muscles in their wrists. Using a small, vice-like weight machine, they completed multiple, strenuous, eccentric contractions of those particular muscles. ...

After a month, all of the volunteers returned to the lab, had their casts removed and repeated the original measures of their muscles.

As expected, the volunteers who had not exercised showed considerable muscle atrophy now. Their left wrist flexors were more than 20 percent weaker, on average.

Those muscles also had shrunk in size, dropping about 3 percent of their mass.

But the group that had exercised their right wrists’ flexor muscles had maintained almost all of those muscles’ original size and strength on the left.

The benefits were quite specific, though. These same volunteers’ wrist extensor muscles, which had not been exercised in their right wrists, were atrophied on the left.   ...

And the entire process seems to involve more than just muscular mirroring, he says. The sensors placed above the volunteers’ cast-bound wrists picked up some muscular contractions in the left flexors when their right-side counterparts exercised.

“But those contractions were very slight,” he says, and by themselves are likely to be insufficient to keep the muscles healthy and strong. 

He believes that there could be changes in the nervous system during unilateral exercise that somehow reach and change the same body part on the other side.
--Gretchen Reynolds, NYT, on a yearning for symmetry