Madonna introduces a new franchise of gyms

Madonna, it seems, is at it again. Long the epitome of the cultural maven, consistently setting trends for decades, she looks set for another chameleon moment.

This time, it seems she's about to reinvent herself as a kind of post-modern Jane Fonda with a new franchise of gyms. Hard Candy Fitness - her health club, which opens in Mexico City on November 29 before a proposed worldwide roll-out - seems a lot less fun than the album after which it is named. The press release makes it seem rather dull: there's no mention of fitness classes performed in the style of Vogue. Just a lot of cardio kickboxing, a bike studio and terrifying-sounding exercise machines. We'll have to wait to see what the co-founder Mark Mastrov meant when he heralded Madonna's "input on every detail, including music, space, light and other design cues".

The new enterprise is a slightly surprising move, not least because Madonna has been widely mocked in recent years for looking like she spends far too much time at the gym. Do the 52-year-old women of Mexico City really want those arms, veins bulging as they "work out" every day? Still, she's not the first celebrity to impose her fitness regime on an unsuspecting public - this can be traced right back to the 1920s, when Charles Atlas first wrote his famous exercise course in New York. But it was hardly a career change: Atlas was already a bodybuilder by trade.

It took Jane Fonda to make aerobics cool - the film star, model and 1960s beauty filmed 23 of her workouts over a 13-year period between 1982 and 1995. They were so staggeringly popular - 17 million copies were sold worldwide - they've been widely credited with propelling the boom in home video recorders. Although one wonders how many men bought this for their wives simply so they could peer over their beloved's shoulders to gaze upon Fonda in legwarmers and high-cut leotards. But the excitement surrounding her latest DVD for - let's put this politely - the older lady, proves Fonda had a lasting impact.

The Barbarella actress was so successful, it wasn't a huge surprise when other celebrities realised that frolicking with an exercise ball was a licence to print money. Cindy Crawford: Shape Your Body didn't, as far as we know, set any hopeful women on the road to supermodel status. Not least because this 1992 video was ridiculously difficult to follow. When even amazon.com - whose own reviews are never less than enthusiastic - says "swimsuit-clad Cindy puts herself through flings and gyrations that show off her body but aren't any good for anyone else's", you know something's up. Yet it didn't stop the video becoming a huge success.

Indeed, it's probably easier to list the female celebrities who haven't actually indulged in a fitness video. Those who do fit broadly into three categories. There are the women who have had every move of their spectacular weight loss discussed in minute detail by the gossip mags (Vanessa Feltz, Natalie Cassidy and Hannah Waterman) and therefore give succour to those who are also, how shall we put it, unhappy with their size. Then there are the "mature" pop stars who pass on the secrets of how their figures remain formidable despite their advancing years (Cher, Paula Abdul, er, Coleen Nolan). And finally, there are the younger celebrities who have amazing bodies anyway and prance around onscreen as if it was the easiest thing in the world to keep fit (Pussycat Dolls, most of the Spice Girls). This has always struck us as cheating - we can't help feeling that the reason why these people are fit is because they're obsessed with the notion that, as Lady Gaga memorably told Vanity Fair, popstars shouldn't eat.

Some videos, though, are just downright odd. Barbara Windsor shot to fame as the curvy babe in the Carry On films. In recent years, she spent her screen life as the landlady in EastEnders' Queen Vic, which is clearly fertile ground for celebrity fitness DVDs. With the best will in the world, "The Windsor Workout" - which appeared, on screen at least, to consist of chasing people out of the pub, is not an appealing prospect. And neither is the sight of Windsor in a leotard. But such a video not only exists, it features Babs conducting exercises from the safety of a comfortable armchair.

All of which makes Madonna's latest endeavour seem positively well-intentioned. Getting into the groove at Hard Candy might not be such a bad idea after all...