Meet the "Steel Warriors" turning seized knives into free outdoor gyms for London's teens

London — A charity has been hard at work turning thousands of knives taken off the streets of London into a new type of weapon to counter a youth violence crisis facing many British cities. 

In the East London neighborhood of Langdon Park, more than a dozen teenagers met up recently for fitness training on equipment made from the confiscated weapons.

"The thought of doing something that I don't think 1% of the population can do," Bruce Sanh, 16, told CBS News when asked what inspires him to push his body with calisthenics on the recycled weaponry.

The idea is that the community is building something much bigger than muscles. The bars kids climb on in Langdon Park now are made of knives that police have taken off London's streets.  

"It's a whole metaphor for creating positive change out of something that's very negative," coach Demi Alvanis told CBS News.

Volodymyr Hirnyak, 15, said the park has become more than a free place to exercise. 

"Now, I have friends. I have everything now. I'm stronger, I feel more confident," he said. "My wellbeing's better."

More than 10 tons of weapons have been melted down and transformed into outdoor gyms so far under the anti-knife crime initiative "Steel Warriors," which uses the slogan "Put Down, Pull Up, Show Up," to encourage young people to drop weapons and build physical and mental strength instead.

"You see the impact right in front of you, in the moment, when one of the kids unlocks a new skill," Alvanis, who has been training teens for three years, told CBS News. "You can see the ecstasy in their face. You can see their face light up with hope."

The kids say the hope is real.

Rafi Abdur, 16, who also goes to the free weekly workout sessions, told CBS News it had changed his life. 

"Some people cannot afford gym memberships," he said. But the program allows them to "come with their friends and like, work out in parks together," which he said improved their overall well-being.

Hirnyak said it was a great outlet for teens

"I think, because teenagers have too much energy, that they locate [it] into a bad cause. It gives a nice atmosphere, cause, you know, like they used to be bad, like the knives, the metal — it used to be bad, and now it's turned into something really good," he said.

Alvanis told CBS News there's a deep power in pushing yourself.  

"I believe calisthenics should be taught in schools," he said. "We try to create the best opportunity we can and bring them into our circle, especially in those areas that have high risk. I think there should be more of these outdoor gyms. When you're training in these parks, you feel not only a love of the sport that you're doing, but a love of the cause."

As for the future, Hirnyak knows what he wants. 

"I wanna be healthy," he said. "I wanna be strong, so then I can inspire others to do the same."

The Steel Warriors charity hopes to expand its work, building more free gyms across the U.K. and, one day, maybe even in the United States.