I'd like to forget the last time I joined an aerobic class. Billed as light, gentle exercise, it left me feeling like I'd swum the Channel wearing flared jeans and a Puffa jacket.

Gruelling would be an under-statement and at one point I was forced to drop out and sit at the side amid much whispering from the supple young things who carried on fat-burning to some fast and furious Madonna hit.

The next day I didn't feel charged and exhilarated as I'd been led to believe I'd feel. Instead I could hardly move. My legs felt like lead and I couldn't turn my head. It took more than a fortnight to get back to feeling my normal, grossly unfit but pain-free self.

Now doctors are warning that fortysomethings like myself who take up vigorous exercise, such as work-outs at the gym, running or other fitness regimes, could be at risk of serious health problems. In the United States they're labelling it Stone Syndrome, after actress Sharon Stone, who suffered a stroke after training for a charity run.

Now, like many people my age, I don't want to start filling every spare moment with exercise. I hated anything to do with the gym as a school girl - those horrible exercise mats that smelled of sweat, those awful mini trampolines that propelled you in any direction but on to the mattress, and that ridiculous vaulting box that injured around a dozen pupils every lesson.

In the adult gyms of today, the mats may be squeaky clean and the equipment may have changed, but my feelings haven't.

The problem is, we feel pressured. There's a gym on virtually every street corner. They have swimming pools, cafs with comfy sofas, beauty salons, bars and crches that look after your children. They stick leaflets through your door almost daily, offering money off and urge you to pick up the phone and in one fell swoop transform yourself into a new woman.

And people succumb. Just about every woman I know is a member of a gym and the rest of us feel wracked with guilt because we're not. I've even phoned up myself hoping to join the ranks of gym members, believing that the mere presence of the membership card in my purse will make me fitter. The only reason I didn't give in was the ridiculous cost ("Is that annually?" I stupidly asked, about the monthly sum they were asking - WITH the discount).

To be honest, I didn't really want to join, but I feel left out. Even the most sluggish of my friends have been lured by the promise of trim waists, firm busts and smaller bottoms. They haven't had any real exercise since school, yet they eagerly leap on the treadmill, jump on the exercise bike and pump their iron. They feel so awful afterwards that they haven't the energy to make the children's tea.

Like many middle-aged gym-goers, they get no exercise at other times. When they're not at the fitness studio, they're slouching on the sofa, eating curries and driving to the corner shop. And their bodies can't take it.

It's time we stopped behaving like sheep and made a stand against this compulsion to exercise. It's safer - and cheaper - to be like me, and just think about it.