Warning: Obsession with abs is counter-productive

"Training has moved on," says Gareth Cole, head of education at the Third Space gym in Soho. "Core is a word that I hear every day but I believe that the public's view of what it is is completely different from what it should be. Sit-ups and crunches are isolated movements of the abdominals - a lot of people would consider them core exercises, but we'd never prescribe them."

The sit-up suspension doesn't seem to be doing the gym bunnies at Third Space any harm: many of them sport abs to rival Gwen Stefani's.

Jean-Claude Vacassin, the founder of W10 Performance in Ladbroke Grove, agrees. It says: "The focus on core is a massive bugbear for us. There is a place for sit-ups but not for people who spend a lot of time hunched over a desk. If your lower back is often rounded - spinal flexion - you don't want to create more flexion. To say it is all about core training is like looking at the world through a straw."

Given that so many Londoners spend most of their waking hours at a desk, City slickers are exactly the type who need to heed this warning.

Cole and Vacassin's verdict is supported by Dr Stuart McGill, spine biomechanics professor at the University of Waterloo in Canada, who suggests that doing isolated abdominal exercises such as sit-ups can lead to back problems by damaging the discs in the spine.

Christnoel Buhay, sports rehabilitator at Duo Health & Fitness, reckons men are particularly prone to abdominal obsession: "The problem [men have] in the gym is they train everything they see. If they can't see it, they don't train it: bum, lower back, hamstrings. A guy's typical workout would be chest and biceps, so the complete opposite of what they should do. You should [do exercises that] open up your posture, strengthen the lower back and you should avoid over-using the muscles that you're already working."

So which exercises should we be doing instead? All the trainers advise picking those which use a wider range of muscle groups. Cole shows me the Plank Matrix, where you start in the basic plank position but roll onto your side and lift your legs in turn; it strengthens the muscles around the spine and improves posture. Squats, lunges, pull-ups, push-ups and deadlifts also have fans, or, as Vacassin puts it, "the kind of exercises that aren't sexy to talk about any more".

Buhay doesn't think the term "core" should be scrapped altogether, however, but that it needs to be understood more broadly, to mean all the muscles deep within your trunk: "Core is not your abdominals. The deep lower back is more important, the supporting muscles: strengthening and lengthening them." He says the "core" should take in the muscles around the hips, the lower back and the spine, with a strong emphasis on the glutes (the muscles in your bottom).

Cole dubs this "the combined core" and says: "The message is: the core is dead! Long live the combined core!"