So there I was in the park the other day, pushing my son in a swing, marvelling at how much exercise I was giving my biceps (or triceps or Primarks or whatever they're called).
Then all of a sudden, a group of new mums - the collective noun I believe is called 'a wobble' - puffed and panted past me pushing their trendy prams in a buggy fit session.
Dressed in joggers and enormous sports bras, the 20-strong pack herded across the grass in a ground-shaking, earth-trembling mass and then stopped as their instructor, a lean, mean Lycra-ed machine barked orders to "give me 20".
They wheezed through some squat-thrusts using their pushchairs as supports, no doubt urged on by the memory of that slab of cake they had the day before in Starbucks.
Beneath blankets, their babes-in-arms must have wondered what on earth mummy was doing – a new version of peek-a-boo perhaps?
Then off they jogged, leaving a trail of wheelmarks as I stood their open-mouthed at their sadistic quest to fit back into their size 10 jeans.
Have things changed so much in just three years, since I was a clueless first-time mother?
Back then – and it seems so long ago now – we were told 'gently does it' by health visitors when we wondered how on earth we'd get our bodies back. Most of us still looked mid-trimester pregnant for months afterwards and although we moaned about still being in maternity clothes, we didn't ever feel under such pressure to be back in shape so soon.
We were still too busy worrying (or should I say being obsessively neurotic) about our babies than our figures; the pounds would come off eventually, we'd just let nature take its course.
And we were too knackered to even consider any exercise – breast-feeding, nappies and endless trips up and down the stairs to get yet another babygro was quite simply enough for us.
But since then, there's been an explosion of the coverage of celebrity pregnancies and births in newspapers, magazines and on TV. A big wow of 'doesn't-she-look-amazing-considering' goes out on a daily basis, awarded with a whoop to those famous mums who ping back into shape weeks after the birth. It seems the miracle of childbirth is not enough compared to the miracle of being bikini-ready.
Just look at Denise Van Outen, who debuted her slim post-baby body two weeks after giving birth, thanks to a diet of healthy meals being delivered to her door.
What about Tess Daly having a water fight in a two-piece in her garden 10 weeks after having her second child? And how can we forget Dannii Minogue modelling M&S swimsuits a few months after having a baby; Rachel Stevens in skinny jeans 18 weeks post-birth; Gisele Bundchen going back in the gym within two weeks; Angelina Jolie in a LBD 11 weeks after having twins; and Heidi Klum strutting down the catwalk five weeks after having her fourth child.
Of course, some women are naturally slim – we all know mums who stuff themselves silly with cake and never put on a pound. For the rest of us, this celebration of celebrity bodies post-birth just adds to the pressure of losing baby weight too quickly. But how can we compare ourselves to them when we don't have nannies, personal trainers, nutritionists, a gym in our mansion or the wealth to pay for door-to-door delivery diets?
Gentle exercise is all well and good – I'm talking a four-lap walk of the park pushing the pram – but experts warn the pursuit of dropping countless dress sizes when you're only just getting over the birth can put your mind and body at risk.
Helen Rogers, from the Royal College of Midwives, sums it up perfectly: "Women still see these images of celebrity mums as what they should be aspiring to – there's a real issue here about nutrition and keeping fit and healthy when body image is so poor."
In my experience, it seems the best thing a new mum can do is to stick to the 'nine months on, nine months off' approach.
Because as soon as your baby starts toddling, weaving their way to the plug socket with a fork, you'll have a daily 12-hour work-out on your hands.