Isles has been dubbed the fastest man in rugby - he has a 100m personal best of 10.13sec - and it has been claimed that he is quicker than Usain Bolt over 20 metres.

He will be part of a US squad that is being widely backed to make a major mark on the men's rugby sevens tournament, which kicks off next week.

But it could have been a different story altogether, as during the build-up to London 2012, Isles was preparing for American trials - in track and field.

And his blistering pace promises to be one of the Rio sevens highlights if his American team-mates can play their part in allowing him to potentially wreak havoc.

"In 2012, I was getting ready for the US Olympic trials in track and field," he said.

"I was studying, and I came across some rugby. I started watching it, and I thought 'oh man'. It was a tough, tenacious sport, and I thought I could be pretty good at it.

"I looked up Nigel Melville (then USA Rugby chief executive, and now Rugby Football Union director of professional rugby) on Google for his contact information.

"He rang me at five in the morning, and started talking to me, and four days later I packed up all my stuff - I was living in Austin, Texas at the time - and drove to Aspen, Colorado, played rugby there for about a month and then got invited to a US development tour in Canada. I toured there, and the next day, I signed a contract."

While Isles is now among the biggest box-office talents in world rugby, he has got there helped by a ferocious drive for success borne from a difficult childhood that saw him up grow up in an Ohio foster home before being adopted at the age of seven.

"My childhood was a fight and a struggle to be somebody, and not be another statistic," he added.

"When times got rough, it was just having the mindset to keep going. You have got to motivate yourself, and I taught myself that.

"You can be anybody you want to be, but you have got to work hard and have a vision. For me, it's just having a drive to never stop and keep going, no matter how tough it is. Ultimately, it is up to you."

Isles' game-winning quality is not lost on his team-mates, particularly USA 2015 World Cup squad member Danny Barrett.

"The first time I saw Carlin run, it just looked so easy," Barrett said.

"You just don't have a chance. He is so fast, he makes fast people look slow. There are some guys out there who are under 11 seconds for 100 metres, and he makes them look slow. It's unreal.

"His acceleration is so quick. I am sure that everyone has seen that stat that over 20 metres, he is faster than Usain Bolt, so that's a pretty special athlete to have on your team.

"If he's that fast and he has got a ball in his hand, it's unfair. It is kind of like having your trump card. He is one of the guys we can count on.

"People have to play him differently because he's so fast, and that opens up other opportunities for the other guys."