It was a craze started by Jane Fonda a quarter of a century ago and became a lucrative sideline for a succession of stars. Now America's space agency has entered the world of celebrity fitness videos by beaming astronauts' exercise routines back down to Earth.
Nasa is broadcasting the workouts of the crew of the international space station, orbiting 220 miles above the planet, in an attempt to encourage the country's overweight to shed some pounds. The agency hopes viewers of its Nasa TV channel will follow the astronauts' lead - without the unique difficulties posed by zero gravity.
"It's all about motivation," said astronaut Clay Anderson, whose workouts strapped to exercise equipment during his five-month spell aboard the space station last year are among those featured. "You have to set a goal, whether it's new clothes, losing 20 pounds or being in good shape when you land on Earth."
The footage features astronauts using the space station's three fixed pieces of equipment - the treadmill, exercise bike and multipurpose bench - during mandatory exercise sessions of two hours a day.
According to government figures, 57% of adults in the US are overweight and 32.9% are classified as obese. Nasa hopes it can help make an impact on the figures while highlighting the importance of fitness among astronauts, who must withstand the rigours of long space missions and the bone density loss that follows.
"People should know how hard astronauts work," said Anderson, 48, who lost 5.5kg (12lbs) before returning to Earth in November. "When you sweat, it clings to your skin and if you shake your head it flies off. It's not pleasant for the others so we make sure we use towels."
Last April, astronaut Sunita Williams ran the Boston marathon from space, pounding out the miles on the treadmill in four hours 24 minutes as thousands raced the streets of the city. Crewmates cheered her on as the space station orbited at 17,500mph.
"Suni's kind of a crazy case," Anderson said. "I would run for six seconds and say, 'That's it, I've gone 26 miles, I'm done.'"
