Only a block away from the highway to Rio de Janeiro's international airport, busy with foreign tourists, athletes and VIPs during the Olympics, a child sits nursing a submachine gun.

He is one of a ragtag bunch of youths guarding the border between his drug gang and a rival group in the Complexo do Maré group of favelas, one of the Brazilian city's toughest slums. Unwanted visitors can meet a hail of gunfire.

Only a few days into the games, a member of the Força Nacional, a paramilitary police force, was fatally wounded here after he and some colleagues lost their way and drove into the favela by mistake.

"Don't put on your seat belts in the favela," says Luke Dowdney, the British social entrepreneur who founded Fight For Peace, a project in Maré that uses boxing and martial arts to help children develop discipline and self-esteem.

A seatbelt could impede a rapid exit from the car should a shootout begin. "We get shut down on average five to six times a year because of shooting on the street out the front."

Maré and other conflict-ridden low-income communities similar to it in Brazil usually make headlines for their problems with violence and drugs. Yet for all their challenges, they have also become sources for some of the country's brightest sporting talent.

Of Brazil's six gold medals, three were won by people from favelas or low- income communities, including Robson Conceição for boxing, Rafaela Silva for judo and pole vaulter Thiago Braz da Silva, an orphan raised in a humble family.

That is not counting a fourth for football, whose players often hail from poor families. Two of Brazil's six silvers were won by canoeist Isaquias Queiroz dos Santos, an athlete raised in an underprivileged household in the country's impoverished north-east.

"The majority of kids in boxing have had a tough childhood in the favelas and they use this as a source of motivation," said Roberto Custódio, who trained at Fight For Peace and is now a member of Brazil's national boxing team.

Many of these athletes were identified through social programmes such as Fight For Peace. The organisation not only provides children with physical training but also education and support.

Himself an amateur boxer, Mr Dowdney said he had the idea for the project while studying Brazilian street children in the 1990s. The only thing that could persuade hardened glue addicts to stop using the substance was boxing lessons, he said. "This was like a lightbulb moment."

Funded by donors and his own sports clothing business, Luta - which he has since sold to Reebok - he has also set up clubs in London, South Africa and Jamaica.

In Rio alone, his centre trains 2,000 young people a year. It also runs a programme for traffickers, helping them to return to school or enter the workforce. Children who go through his programme were far less likely to reoffend than those who ended up in prison, he said.

"We think that kind of programme should become policy," he said. "These kids have got more in common with child soldiers than they do with gangs . . . we need to rehabilitate those kids."

Fight for Peace has taken on a life of its own. One of Mr Dowdney's students, Alan Duarte, is setting up his own version in another notorious favela, Complexo do Alemão. Competitive bouts are held in a fighting ring with a dirt floor.

"I have friends and family who were involved in drug trafficking, I have lost people close to me who were assassinated," says Mr Duarte. "But because I participated in the programme at Maré, I avoided falling into that life. So I thought, why not bring it here to Alemão."

With the Olympics in town, Mr Duarte was visited by the French rowing team, whom he treated to some short sparring sessions in Rio's sweaty heat.

The games had had little direct economic effect on the favelas, he said, with the tickets unaffordable - the cheapest are $40 - for most. But that did not mean people had not been watching them on television.

"I pass the bars, the barbers, they always have the games on TV, everyone is watching and shouting like mad. They would love to be there," Mr Duarte said.

And given that so many of the Brazilian athletes they saw were competing from communities like their own, that interest was hardly surprising.

Copyright The Financial Times Limited 2016