Alex James, the bassist from Blur, famously said that he celebrated his 20th birthday with drink, his 30th with drugs, and his 40th with food. But these days turning twentysomething is rather different. The only bottles we're swigging from are water bottles and we're popping protein balls not pills. Our LBDs – little black dresses – have been usurped by GDLs "gravity-defying leggings", and we're addicted to avocado on toast, not Class A drugs.
Which all goes to explain why gym birthday parties – once the preserve of hyperactive children –are becoming a hot new invite for young adults. Held in the new breed of supergyms – which are now harder to get into than the coolest bars and restaurants in town – it's seen as a treat to get a group of friends into sold-out classes that otherwise operate waiting lists and one-in-one-out online queue policies.
It's official, there is a new mood for getting sweaty more than getting sloshed. More than a quarter of 16-to-24-year-olds in the UK are now teetotal, according to a 2017 study by the Office for National Statistics, and "mindful drinking'" – however ghastly the expression – seems to be catching on. More than 500 people attended Club Soda, a sober festival in London last year, where the only thing to drink was 20 non-alcoholic craft beers.
A new generation are getting their kicks out of different kinds of highs. Everything from taxidermy classes to life-drawing and lampshade-making have surged in popularity, partly because people are hankering after experiences and also because you can do all these things un-drunk.
In the last year, gyms have upped their game, reinventing themselves as cool boutique affairs or exercise emporiums. Some of them turned the lights down and the music up and started feeling like the nightclubs my generation have slowly stopped going to. Even gym wear has practically become haute fashion.
With gyms feeling more like nightclubs, it's no surprise that they have been getting a lot of calls about birthday parties.
Healthy over hangover
The idea is that you and friends pay for a themed, instructor-led workout, or aerobics routines built around party games like pass the parcel. If the gym has a restaurant you can even have a birthday lunch or dinner of "healthy" pizza (salad leaves replacing the dough) and raw vegetable juice afterwards, going home on a natural high. In previous years, you would have spent roughly the same amount getting into a club, around $200 on booze and cabs, and woken up with a hangover.
Frankie Bennett, 25, the co-founder of The Hard Yard gym, says: "Lots of millennials are drinking less and even if they're not, they're sick of sitting in pubs and want to do something a bit different for their birthday.
"They want to feel good afterwards and while you used to be quite excluded from the party scene if you didn't drink, there are more options now." But really? How are my friends going to react to an invitation to an 11am workout party at the weekend? As soon as I start asking people, everyone seems to be going abroad. Others are more frank. "I really shouldn't commit," my friend Laura tells me. "I nearly passed out from climbing some stairs earlier."
It was therefore to my great surprise and gratitude that 10 of my friends did finally agree to turn up at a GymBox in central London to sweat it out for my birthday, albeit some of them sweating out booze from the night before and others sweating purely from the thought of socialising without it.
"I often celebrate my birthday by inviting my friends to get scantily clad and sweaty, although not at a gym," Ellie, 25, tells me, promising to turn up in her best activewear, "which is seldom used for working out". Polly, 27, also tells me she'll make a special effort – by washing the mud off her trainers. Max, 24, says: "This is the stupidest thing I've ever heard of," but at least agrees to show up.
When they arrive, the atmosphere at the gym puts them at ease. "At least it sounds like a club," Hugo comments, wincing at the huge speakers that are blaring house music at muscular people on treadmills. In the studio itself, we plug an iPhone into a sound system which makes it feel like a normal party, almost. "Is there any beer?" Max asks while we jog on the spot in party hats, but I have to explain that the idea is that we get a sober rush of endorphins from the exercise rather than the alcohol. "Protein ball?" I offer.
The games, all based on kids' party games, at least manage to cheer them up a bit. Harry, 24, went to a party run by The Hard Yard – a fitness class run by former convicts – in October, and is already a huge fan of "planking lions", a torturous version of "sleeping lions", where instead of pretending to be unconscious for as long as possible, you hold your body in a press-up position on the floor until every muscle you didn't know you had judders with the strain and you crumple into a heap.
Other games include pass the parcel, with all of us jogging on the spot until the music stops and then one lucky guest unwrapping a layer to reveal a "prize": instructions to do 20 press-ups, sit-ups or burpees.
It's during a version of "musical chairs" involving squatting for as long as your quads can bare when the music pauses, that someone suggests being made to ache like this on your birthday is a cruel way to remind yourself that you're getting older.
By the time we play "Simon Says" at the end of the hour and have to start swinging dumbbells, we decide it's time Simon let us go to the pub. There not being a healthy restaurant at the gym, we settle for chicken burgers down the road, but, amazingly, most people don't want anything alcoholic when we get there.
After a decade of birthdays in pubs, it is refreshing to take alcohol out of the equation. "It was slightly embarrassing to be encircled by a group of people playing pass the parcel while my abdomen convulsed with the attempt to do something called a V-sit, but I feel so good now," Ellie tells me.
Even Max finds he hasn't minded it much. "It was a nice change to have the rest of your body hurt after a birthday party rather than just your head." I couldn't agree more.
The Sunday Telegraph, London