RIO DE JANEIRO • An Olympic swimming pool is 50 metres long. The fastest human beings on the planet cover the distance in about 22 seconds of fury.

The 50m freestyle is not an event for smooth perfectionists: it is a kinetic blur, an assault on physics.

It is about overcoming resistance, about making every second count, about cramming into that short space as much as you possibly can.

And as Anthony Ervin swims, so he has lived.

At 35, Ervin will be the United States' oldest swimmer at the Olympic Games in Rio de Janeiro. In fact, he is the oldest American man to swim in an individual event since 1904.

This is his third Olympics - he competed in London four years ago and in Sydney as a 19-year-old.

Stretching between these markers is a life story that might be the most extraordinary of any of the 10,500 athletes competing in Rio - a spiritual journey of self-discovery that has left its mark on Ervin via the osmosis of experience and the ink of the tattoo gun.

The 2000 Olympics made him a star. But stars have a gravity so powerful that sometimes they implode, as Ervin would attest.

Tall, photogenic, he had a scholarship at Berkeley and a world record in his pocket. But, beneath that conventional frame, a maelstrom was swirling, as he struggled with the dehumanising discipline required by elite sport.

"I was in a state of rebellion," he says. "As soon as something appears before me that seems like its sole purpose is to control me, I will fight it, and for a while that was the pool."

Further complicating his feelings was the relentless media attention, much of it focusing on his status as the first swimmer of African-American descent to win an Olympic gold.

His life started to unravel as he began to drink heavily and experiment with drugs.

In 2001, he won the 50m and 100m freestyle at the world championships. But, while his ability to speed through the water remained supreme, privately, he was sinking.

"I felt very alone and isolated, a man atop a mountain who couldn't receive help from other people," he says. "I felt like they didn't understand.

"That loneliness became a dark well into which I plunged deeper and deeper until I no longer recognised who I thought I was and how I was seen by other people, the value that was being posited on me through a thing such as athletic prowess. It just seemed so pointless that that seemed to be what my existence was, so I just wanted to hit a reset."

It was at this dark moment that he tried to commit suicide by taking an overdose of tranquillisers. But the next morning, he regained consciousness. He resurfaced. He was alive.

"In one way, the suicide worked," he says. "A part of me that I didn't want any more did die, and what was left was a state of being reborn. Before, I couldn't move, I had become chained to the idea of who I was, shackled to the point of paralysis; and afterwards I was free."

Liberated, he quit swimming and college. He sold his Olympic gold medal, donated the profits to the Unicef tsunami relief fund, grew dreadlocks, converted to Zen Buddhism and moved to New York to join a rock band called the Weapons of Mass Destruction.

"The band was one of my best friends," he says. "The music became my way of telling myself that I can move beyond these shackles, these prisons of will that I see around me."

Having made his jailbreak from competitive sport, Ervin might never have returned, had it not been for a chance invitation to teach children at a friend's swimming school.

"I found that I wasn't only there to teach those kids; they also taught me," he says. "And probably the most important thing was that sense of play, that sense of joy, that sense of freedom which comes with loving the water."

With a sharpened sense of priorities, he re-enrolled at Berkeley to do an English literature degree and began swimming again - a process he found so cathartic that he wrote a long essay on it that became the basis for his autobiography, Chasing Water.

A year and a half after resuming serious training, he was in London for the Olympics, where he finished fifth in the 50m freestyle.

At the 2013 world championships, aged 32, he swam his personal best time of 21.42sec. At last month's American trials, he swam 21.52sec - the fourth-fastest time in the world this year - to qualify for his third Olympics.

In an event in which some of his competitors are less than half his age, Ervin is a genuine gold-medal contender. It seems that age is just another rule book that does not apply to the last of swimming's mavericks.

Sixteen years after he stood on the blocks in Sydney, the man who swims in a straight line better than almost anyone on the planet has come full circle.

"I have not actually gone too far from where I started, but I can see clearly now from where I came, where I stand, and who I can be," he says.

THE TIMES, LONDON