A long-standing peculiarity in Russian president Vladimir Putin's walk — with his right arm held almost immobile, while his left arm swings freely — has sparked speculation over the years about its origins, with rumors ranging from an in-utero stroke to a childhood bout with polio.

Now, a new study by a group of neurologists reaches a very different conclusion, pinning the source of Putin's gait on the training he received while he was in the Soviet Union's KGB, the nation's national security agency.

In the study, published online today (Dec. 14) in the journal The BMJ, the researchers discovered that several other prominent Russian officials displayed a similar gait, which they say could also be linked to KGB training intended to keep a man's "gun arm" close to his holster, ready to draw a weapon at a moment's notice. [Video: Is KGB Training To Blame for Putin's Stiff Arm?]

Walk this way

When most of us walk, we naturally swing our arms at our sides in opposition to our legs' movements — and we do it without even thinking about it. Scientists have questioned whether swinging our arms actually benefits the way we move, and some studies have concluded that arm swinging in runners helps to maintain balance and conserve energy.

But swinging only one arm is unusual, said Bastiaan R. Bloem, a co-author of the new study and professor of movement disorders neurology at Radboud University Nijmegen Medical Centre in the Netherlands. In fact, an immobile arm is one of the earliest known indicators of Parkinson's disease, he said.

After a colleague sent Bloem an email about a YouTube video showing Putin's stiff right arm, Bloem was intrigued enough to dig a little deeper, he told Live Science. He found a number of videos showing Putin at public events where he walked for long distances. The lack of arm movement had persisted across years.

"You could say, if it were one occasion, maybe he just had a painful shoulder or some other intermittent problem," Bloem said. "But then we discovered this was a consistent finding stretching out over a period of multiple years."

Bloem and a number of his colleagues practice a subdiscipline of neurology that identifies them as "movement disorder enthusiasts." As the term suggests, analyzing how people walk is second nature to these specialists — at neurology conferences, they're the ones evaluating how everyone else ambles across the room.

"Normal movements are complex, and then seeing how they go wrong, when there are defects in the brain, is a fascinating area," Bloem said.

Footage of Putin's walk intrigued Bloem and the study co-authors. But it didn't take long for them to rule out Parkinson's as a cause for Putin's unusual gait. Parkinson's is a progressive disease, and in footage separated by years, there was no evidence that the movement of Putin's arm, or of any other part of his body, was getting progressively worse.

In fact, all evidence seemed to indicate that overall, Putin is in fine physical shape. The researchers evaluated footage of Putin performing a number of different activities, and pronounced his motor skills "excellent."

It was then that Bloem discovered that Putin wasn't the only Russian official walking this way.

Back in the USSR

The researchers observed similar walking patterns — a stiff, nearly immobile right arm accompanying otherwise normal movement — in four other prominent Russian officials: Prime Minister Dmitry Medvedev; former Minister of Defense Anatoly Serdyukov; Sergei Ivanov, chief of the presidential administration of Russia; and Commander of the Western Military District Anatoly Sidarov.

Other footage and photographs that the scientists examined showed that the Russian officials were all right-handed and did not appear to suffer from any impairment of their right arms, except as exhibited while they were walking.

That, Bloem told Live Science, was when things became "reallypeculiar."

The odds of all five Russian officials suffering from Parkinson's and exhibiting precisely the same symptoms that appeared on the same side of the body and at the same stage of degeneration were slim. Bloem and his colleagues knew there had to be another explanation, and they found it — not in medical literature, but in the pages of a KGB training manual. [3 Myths About Parkinson's Disease]

"It literally says, when you're walking, don't move the right arm, keep it close to the holster and be ready to draw the gun," Bloem described.

Putin and Ivanov both served in the KGB, where they would have doubtless been trained "by the book," to restrict their right arm movements while walking. And although the other officials were not KGB, their military backgrounds could explain their adopting this particular gait.

For Medvedev, the only official with neither KGB nor military training, the study suggests that his reduced arm swing could be an example of "imitating the boss," a practice not uncommon in Russia, where officials frequently absorb mannerisms of their superiors, according to the researchers.

"Fascinating and complex"

The study authors found more examples of this weapon-ready walk in another unlikely location — Hollywood movies about rough-and-ready "wild west" gunfighters. Like the Russian officials, actors portraying gunslingers in old-time westerns displayed a similarly immobile right arm when they strode down Main Street at high noon.

The researchers concluded that although Putin's movements appear to be the result of conditioning, and not an example of a neurological disorder, the study is still valuable to those who study diseases like Parkinson's, Bloem said. By drawing attention to this trait as a symptom of Parkinson's, the new study could help doctors identify Parkinson's earlier, and prevent the full-blown disease from developing.

And reporting it with a touch of whimsy doesn't hurt either, Bloem added.

"It's a tongue-in-cheek, semi-funny paper, but there's a very serious message behind it as well," Bloem said. "Teaching moments tend to stick best if they're presented in a humorous way."

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