Michael Phelps competes in the 200-meter butterfly semifinal during the Rio Olympic Games in Brazil on Aug. 8. (Jonathan Newton/The Washington Post)

When truly superlative swimmers like Katie Ledecky or Michael Phelps take to the water, their movements seem inhumanly graceful.

If you took a look at the complex choreography between the swimmers' brains and their muscles, the whole thing would look even more impossible. A stroke may look rhythmic, but it's made up of hundreds of different muscle movements, a cacophony of electrical signals shooting down from the brain through the spinal cord and out to control many tiny twitches. Thousands of brain cells coordinate the precise contractions of muscles, duplicating motions honed with years of grueling practice. And yet in the midst of this impossibly intricate series of muscle twitches, there remains a strange rhythmic quality, scientists say — a hidden beat in the electrical pulses of the brain.

Just as Phelps follows a rhythm with his strokes, his brain is repeating a pattern over and over again that keeps his muscles coordinated — even as they perform minute movements that don't seem cyclical at all.

That's according to Mark Churchland, a neuroscientist at Columbia University’s Zuckerman Institute and Grossman Center for the Statistics of Mind. Churchland studies the brain activity behind voluntary movement — motions we choose to make of our own accord — and swimming can serve as a great example of that.

"With something like walking, it's known that the spinal cord itself can produce a lot of the rhythms you need, in many animals and maybe in humans," Churchland told The Washington Post. "But swimming is obviously completely learned."

The freestyle stroke that Ledecky so excels in didn't really exist a century ago (at least in competitive athletics) and Phelps's signature butterfly is an even more recent invention. Humans may have evolved to be reasonably decent swimmers — we're pretty good at not drowning, given a little bit of instruction — but we certainly didn't evolve to swim like that.

"It's not automatic, it's not something evolution gave you," Churchland said. "It's something the very human parts of your brain need to slowly learn to do."

Like most in his field, Churchland used to focus his efforts on the motion of reaching. It's fairly simple and incredibly common, and serves a clear-cut evolutionary purpose, but it's purely voluntary — so it makes a good model for studying movement as a whole. But when Churchland and his colleagues started looking into more rhythmic movements, they found, to their surprise, that many motions that seemed less than rhythmic from the outside — reaching, for example — actually produced cyclical signals in the brain.

Picture a sort of record player, holding a record with dozens of grooves. Each groove gets its own needle, and as the record spins around once — a single cycle — the motion of those needles, determined by the depths of their particular grooves, control the movement of dozens of corresponding muscles. Some will burst once, some twice. Some earlier, some later.

An arm reach, Churchland explained, isn't just a single turn of the record. It's more like a turn and a half. Even though the act of reaching out with your arm seems to be a motion with a single start and end point, there's a moment during the motion when your brain starts the electrical signals over again. (In mice, anyway — we haven't quite proved that humans are exactly the same.)

"That central rhythm, which is a very simple 'go around, go around, go around' is capable of coordinating the remarkably complex and heterogenous movements of muscles, which all have to do different things at different times in different ways," Churchland said. "In some sense, an athlete like Michael Phelps has trained the grooves in the record to be exactly the right grooves."

That doesn't mean neuroscientists have any idea what makes these champions so good at what they do.

"That's a question we really can't answer right now," Churchland said with a laugh. "Or at least I'd give you worse answers than any good swim coach could give you."

But take heart, non-Olympians: Even if your body can't produce record-smashing swim strokes, it's still an incredible piece of machinery. We all have a system, Churchland said, that's been perfected over "eons of evolutionary time." Your 100-meter freestyle might be a little sluggish, but the electrical signals that your body to move zip from your brain to your muscles with shocking speed.

"You've been selected to have this incredibly direct connection, this incredibly fast pathway," Churchland said.

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