Running, leaping and flying into the unknown are attracting a growing band of followers around the world, ready to risk life and limb for the ultimate adrenaline rush.
From base jumping -- where devotees jump off a cliff or tower with a parachute -- to wingsuit divers who fly in a birdman jumpsuit, to highlining -- walking across a rope at high altitude -- the sky has become the limit for extreme sports.
The death toll has also taken off.
About 20 people a year are now killed base jumping or in wing suits. The United States and Switzerland have had the highest casualties, with each recording more than 50 deaths since specialist groups started keeping statistics in the 1990s.
In France, four jumpers have lost their lives since the start of August.
Numbers have gone up along with the popularity of the daredevil pursuits. And both followers and victims have become ever more high-profile.
In August 2013, British stuntman Mark Sutton, who parachuted into the London Olympics opening ceremony dressed as James Bond, died in a wingsuit accident in Switzerland after jumping from a helicopter.
American Brian Drake, one of the leading international wingsuit fliers, died along with well known French and New Zealand jumpers, Dan Vicary and Ludovic Woerth, in April.
The three leaped from a helicopter thinking they were jumping into a gorge, but fell onto an Alpine pasture before they could open their parachutes.
Once limited to a small club, extreme sports have taken off as technology develops and restrictions or security constraints in everyday life become ever tighter.
Bungee jumping and delta plane gliding were the frontiers until the 2000s when the rise of social media brought the really extreme sports out of the shadows.
"Today a lot of the people in these sports put themselves in videos, and that changes everything," said Nicolas Cazenove, a specialist in clinical psychology and health at the University of Toulouse-Jean Jaures in France.
Now videos of wingsuit jumps down mountainsides are all over the Internet.
- Risk seekers -
"There is a narcissistic side that did not exist in the past when the practices were more closed," Cazenove added.
"The risks are being increased because once everyone has done something spectacular, you have to move on to something even riskier."
The technology and the equipment for extreme sports are now widely available.
A wingsuit jumper leaps from a plane or off a mountain in a suit that adds surface area to the body, enabling the jumper to glide like a bird before opening a parachute to complete the jump safely.
A wingsuit can be bought for as little as $500 (375 euros), and a beginner's course for $1,950. It can take years to master the art safely, however.
Austrian daredevil Felix Baumgartner went up 39 kilometres (24 miles) into space to jump to Earth in a pressurised wingsuit, making global headlines in October 2012.
One year later, Alexander Polli, an Italian-Norwegian daredevil, leaped from a helicopter and reached speeds of up to 250 kilometres (155 miles) an hour as he hurtled toward and through a cave opening in Spain barely wider than he is tall.
"There is an unbridled inventiveness," Cazenove said.
"Also our society is imposing more and more physical protection and speed limits on everyday life and in sport. Extreme sport followers are looking for niches" in the rules, he said.
- Overwhelmingly male -
Cecile Martha, a researcher in social psychology at the Institute of Movement Sciences, Aix-Marseille University, monitored about 40 base jump followers -- out of about 200 registered in France -- for 18 months.
Martha, a specialist on risk-taking in sport, said that nearly all are males "who feel the need for powerful, higher than average sensations."
"They are not impulsive, however," the researcher added. "They go about it in a very meticulous way, and those who have the most accidents are the impulsive ones."
Cazenove also said that base jumpers and wingsuit flyers "do not get enough highs from daily life."
"More than seeking a confrontation with death, they have a desire to feel extremely alive," the psychologist said.
Experts note a big difference between extreme sports and those like Formula One and motorcycle racing which have long been considered dangerous.
"There are mortal risks in horse jumping, skiing, gymnastics, Formula One, sailing, motorcycling," said Jean Griffet, a sociologist and specialist in water extreme sports such as apnea deep sea diving.
But the risk is reduced by crash barriers, padding and other measures and the sport is progressively learned, said Griffet.
"Extreme sport does not have this apprenticeship. When you base jump for the first time it is already a lethal activity, ruled by the law of all or nothing."