Older parents may be mentally prepared for kids, but physically? Deborah Holder discovers an epidemic of back pain and injuries
"Hangovers are the worst," says Sylvie with conviction. "Worse than the injuries and the exhaustion. I used to be able to enjoy a night on the tiles and function fine at work the next day after two hours sleep and a couple of Paracetamol. Now it'

s just not worth it. The kids are merciless and my body's just not up to it. It can take me days to recover; meanwhile I'm too ill to look after them and they're a danger to be with when my defences are down."

Sylvie is 42 and the mother of two boys aged two and four. She suffers from semi-permanent back pain, terminal exhaustion and doesn't remember the last time she didn't have a cold or sore throat. She's one of a growing number of parents who delayed having children until their late thirties or forties and are paying the physical price.

The heart-warming benefits of delaying parenthood have been well documented. Psychologist Julia Berryman of the Parenthood Research Group, Leicester University, found older couples were more stable, financially and in a relationship, better informed, more likely to have fulfilled themselves before the birth and so less likely to expect children to do this for them, less likely to use physical punishment and more ready psychologically for the demands involved. Psychologically maybe, but how about physically? The average age for first babies has risen steadily and the age groups where birth rates have increased most are 35-40 and 40 plus. A side-effect of starting late is that couples tend to have a few children in quick succession, meaning many oldstershave not one little cherub making demands on their creaking frames but two or three, and all under five. Untroubled by the biological clock, six times as many of these oldsters are men. Derek, 46, is the proud father of three: two-year- old twins, Dilysand Artie and William aged four.

"I was leading a life of sloth and decadence before the kids," says Derek. "It was a please-yourself existence. I spent most of my time conserving energy under a duvet and the rest having parties." Once a sheep farmer, Derek was previously quite fit. Hiscurrent working life as a dealer in secondhand books with his own shop to run, combined with his role as father of three, has led to back problems and sciatica.

Derek's wife Janet, however, feels she is fitter than she's ever been. "The only health hazard I can think of is that your chances of twins increase with age."

Clinical physiologist Dr Kenneth Collins says dramatic change doesn't usually occur until the seventies but a less noticeable shift can start much earlier. "Modern life tends to fix people in their chairs in front of the television much more than it usedto and even in the forties it starts to show." Dr Collins believes the crucial factor is not just age itself but the lifestyle people settle into during the pre-baby years. Having been carefree and active and in our twenties, it's downhill f rom then on- a sedentary job and a comfy sofa soon replace the exertions of Eurorail adventures and the football pitch. As we age, we slow down - reaction times are a typical example - but change is usually imperceptible. It's only when you introduce a couple of demanding toddlers into the equation that you become aware of what's been going on while you were looking the other way. As Sylvie found to her cost, you're not so much old as out of practice. Last year she had to get her front tooth repaired a fter a runin with a very small Doc Martin. "I just don't have the reactions any more. One minute I was pushing Oscar on the swing, turned the other way for a second and baff! I used to play club-level table tennis. I was fast - now I can't even avoid an oncoming child."

Introducing kids at a late stage can also catch your immune system with its pants down. A decade in the rather sheltered world of the "dinky" results in an immune system unprepared for attack by the endless viruses children spread so efficiently. Recovery time can also be slower if you're not in good shape, says Dr Collins, "and you've had more years to abuse yourself by the time you reach 40". Parents also lose the relax-and-recover activities they took for granted. "The traditional Sunday gets bustedup," says Derek, misty-eyed at the memory. "Instead of breakfast, a leisurely read and Radio 3 you end up watching Postman Pat and throwing the papers away three weeks later - unread."

The most common problem for the oldster is a bad back. The activities associated with babies and toddlers - bending to change nappies, lifting crying babies from their cots, turning and twisting to force the wriggling little darlings into their car seats- seem specifically designed to wreak havoc with the spine. "Sometimes I bend over the bath to do their hair and I can't get up again," says Jacqui, 38. "Doctors tell you not to do too much lifting but - get real!" Osteopath Graham Mason agrees the backtends to become more vulnerable with age and sympathises with the difficulties parents face. "The older parent is more vulnerable because there is a certain amount of degeneration that occurs from fairly early ages - already in the thirties an X-ray will reveal quite a bit of wear and tear. Most wouldn't have any symptoms at all but give them a one-year-old to run around after, a 10-pound baby to pick up, especially if it's crying in the middle of the night, and you've got problems."

The Pirates Playground at the Michael Sobel Centre in North London presents the oldster with the ultimate challenge. Here, around 40 ecstatic kids tear from level to level of a massive "soft play" assault course. Vertigo-inducing slides erupt from tiny gaps and strategically placed tunnels connect one gladiator-like activity to the next. It is kid heaven and the oldster's worst nightmare. "I'm looking forward to virtual reality so that I don't have to actually endure this for real," says Maur ice, whosetwo boys drag him there most weekends.

He sprained his wrist a few months ago and his wife had to be freed by a sympathetic nine-year-old after getting jammed between levels as she tried to keep up with her three-year-old. Staff say they are often called upon to retrieve children from the upper levels when parents aren't up to the climb.

The purpose of such excursions is to wear the little darlings out so you can settle down with the Sunday papers. It rarely works out that way. "They go to bed at about 7.30, we eat around eight and from the minute I swallow the last mouthful my backside becomes one with the sofa." says Julie, 41. "We don't even answer the phone after nine. Friends our age without kids just don't get it - but we're too tired to be coherent."