A doctor has warned teenagers not to copy what they see on television after a 15-year-old was injured trying to jump seven feet between two walls.
Youngsters are warned Parkour takes a lot of discipline
The youth from Pitsea seriously injured his leg on one of the walls when the "free-running" attempt failed.
Dr Donald Law, of Essex Emergency Care, said he was concerned about the increasing number of youngsters trying the new sport craze.
"These injuries can lead to problems of skin and muscle damage," Dr Law said.
Free runners often use a disciplinary movement known as Parkour, which originated in France about 20 years ago and combines gymnastics, break-dancing, vaulting and climbing actions.
Running over rooftops
Those who practise it are often influenced by television adverts and films such as Spiderman and Matrix, which feature actors running over rooftops and jumping from one building to another.
"This is not the first time we have seen youngsters with nasty injuries who are trying to copy what they see on television," said Dr Law.
"Whilst we would encourage people to have an active lifestyle, they need to think about the sort of exercise they take," he added.
"Those who are filmed doing it almost certainly prepare each jump meticulously and are generally extremely fit which reduces the chances of injury, but it is still a high risk pursuit."
Paul Corkery, from the Urban Free Flow organization based in London, described free running as "a way of expressing yourself" saying it can be dangerous only if "in the wrong hands".
"We take such a strong view on learning the fundamentals," he said. "If you know the basics then you're not going to get any more hurt than if you ride a bike.
"It's not an extreme sport - it's very similar to martial arts, it takes a lot of discipline.
"The people who do it properly don't take any risks at all. We take calculated risks and there's a lot of preparation."