They were promised the body beautiful and their mantra was “No pain no gain”. Two decades later they are feeling it again — in their knees, hips and lower backs. They are the casualties of the aerobics boom.

The craze began in the late 1970s but it was the actress Jane Fonda who really got people moving. Following her lead, thousands climbed into Spandex, donned headbands and twisted and punched the air in church halls across Britain.

Now they are more likely to be seen in physiotherapy. Nicki de Lyon, of Sports and Spinal Clinics, London, said: “They have knee and hip and lower back problems. It was not just the constant impact on hard floors, which put pressure on joints, but the twisting movements. And in the 1980s there had not been any research into the right footwear.”

The fitness industry was in its infancy. Robin Gargrave, of the YMCA, said: “People didn’t know what they were doing. They were just following America. Now we know that jogging on the spot waving your arms in the air isn’t the best thing for your body.”

Derrick Evans, who went on to become Mr Motivator, visited a leisure centre in Harrow in 1981 and saw hundreds of women doing “Popmobility”. He hired the two women leading them and set up a class at a church hall in Neasden.

“After a few months I decided I could do this,” he said. Before long he had become the presenter Gloria Hunniford’s trainer and was motivating millions of viewers on This Morning. “In those days it wasn’t critical to have qualifications. There weren’t really any around.” Now 54, he claims to be “fitter than a fiddle” — but his routines were always “moderate”. Others were less so. Andy Jackson, of the Fitness Industry Authority, says that, in the first flush of the craze, “a lot of deconditioned people suddenly started exercising with the intensity of Linford Christie”.

Disciples were told that pain was good for them. “It’s positive pain, just like childbirth,” devotees in America shouted. As the craze took off in Britain, Geri Livingston bought a cat-suit and joined an energetic group in a church hall in Cheshire. All through the 1980s she sought out the toughest classes, attending up to four a week. “My knees just kill me now,” said Mrs Livingston, now 44. “I can’t jog any more, and I have lower back problems.”

Hardest hit were the instructors. “I would be taking 20 classes a week,” said Ebony Williams, who now teaches Pilates. “My knees are painful and swollen, I’m seeing a chiropractor for my back, and I have to have regular massages. All the instructors I knew have had the same problems with their knees, back, joints and shoulders.”

Aerobics is now in decline. In Britain it has been supplanted by a bewildering array of low-impact routines and “conditioning” programmes aimed at people in their mid50s. There, in softly lit studios, next to Japanese fountains and no longer wearing Spandex, the walking wounded of the aerobics boom may seek to soothe their battered bones.

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