Who would want to be in your shoes? Seriously, take a good look at the way you decorate your feet, and unless your choice of footwear can banish cellulite, flatten a dowager’s hump or create an ironing-board midriff, you are doing your feet (and body) a big disservice.

During the past couple of years, a sort of functional footwear phenomenon has spawned a hugely competitive market for sandals and trainers that promise far more than just comfort and style. Where once we were encouraged to try Pilates or yoga to improve posture or lose weight, now it seems that all we need to do is change our shoes.

The most recent sensation is the FitFlop, a thigh-toning sandal whose devotees are convinced that it gives them longer and leaner-looking legs. The FitFlop website apologises for the current limited availability of the sandal, which is due to it “selling out faster than you can say gluteus maximus”. The shoe’s manufacturer claims that its “uniquely built mid-step is designed to tone thighs, activate muscles and tone the calves and gluteal muscles” as well as to reduce joint strain by “recreating the gait of barefoot walking”. The way the sole is shaped, say its promoters, makes the foot unstable, thus encouraging more movement than usual. And by raising the middle of the shoe, it helps to prevent collapsing arches.

But are these promises of lithe and lengthy limbs a step too far? “As with a lot of these fashionable, quasi-medical shoes, I am concerned that people will think that they put them on and turn into Cameron Diaz,” says Trevor Lewis, a consultant physiotherapist specialising in feet and lower limbs at Knowsley Primary Healthcare Trust in Merseyside. He shares concerns with other experts, who say that there is no evidence to suggest that FitFlops are better for the feet than any other flip-flop, and that, in fact, both can cause problems. Because of their flatness, they can cause Achilles tendonitis, for example, as well as pain in the lower leg and calf muscles. “As with all shoes, including high heels, a certain number of people will find them comfortable, but for some they could cause problems.”

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A period of transition is needed with any style of flip-flop, says Lewis, and anyone who goes straight from wearing trainers or high heels to flatties risks pain and strain in the Achilles tendon above the heel. “Keeping flip-flops on also requires a clawing action by the toes that does work muscles, but it can cause pain in people not used to it,” he says. “They can be comfortable for some, but not everyone will benefit from them.”

When it comes to MBT (Masai Barefoot Technology) trainers, the clumpy and somewhat unsightly shoes that are firmly established as a celebrity foot fashion, the arguments for and against are more definitive. Last year more than one million pairs of MBTs (costing around £129) were sold in more than 20 countries; there are now 133 stockists of these bizarre-looking walking shoes in the UK alone.

What makes them different from a regular trainer, the manufacturers claim, is their unique curved sole, which promotes instability and encourages a rolling front-to-back action when someone walks in them. Marketed as “the first footwear that has a positive effect on the entire body”, they are said to assist in eradicating everything from cellulite and bunions to back pain.

Indeed, several physiotherapists claim that the hype is true, and it is supported by small studies at Sheffield Hallam University, the University of Calgary in Canada and Edinburgh Royal Infirmary. “People with back pain will certainly benefit from wearing MBTs because they improve posture and can be helpful for problems as diverse as bunions and osteo-arthritis,” says Joshua Wies, a Cambridge-based chartered physiotherapist (and, it should be said, the director of the MBT Academy). “They do improve the way that you walk and stand.”

But Sammy Margo, a spokes-person for the Chartered Society of Physiotherapy who wears MBTs regularly, stresses that they are not suitable for everyone. “They can possibly help people with stiff backs who do jobs that involve a lot of standing, but for anyone who spends a lot of time at a desk, or has hyper-mobility in their spine and weak core stability, they could make postural problems worse.”

Results of a recent study into the effects of the rocking shoes – one of the few to be published (in the Medicine & Science in Sports & Exercise journal last year) – were inconclusive, with the Calgary researchers finding only a negligible difference in the reduction of pain among osteo-arthritis patients who wore MBTs or good walking shoes.

Nicki de Leon, a consultant physiotherapist at the Sports & Spinal Clinic in Harley Street, is “not a fan of them at all”, because they can “fundamentally alter the way people walk, shifting their normal bio-mechanics so that instead of striking their heel to the floor and transferring the weight forward, they are being rocked forward by their shoe”. That, she adds, is bad news, especially for people who wear them to walk for long distances, such as to work, because “when they take them off their muscles forget what they are supposed to do naturally”.

Despite such scepticism, consumers are prepared to defend their favourite footwear’s functionality. Fans of Crocs, a welly/clog fusion that was originally designed as boatwear, swear that they are not only comfortable, but also exceptionally good for the feet. Last week Harold Glickman, a former president of the American Podiatric Medical Association, described them as “offering more support than flip-flops, which don’t provide a lot of arch support and are open-toed”. Some models have an anti-bacterial lining to prevent fungal infections.

What to wear on your feet, then, has become a troublesome decision. Does one plump for function, fashion or comfort? “There is no rule and no one type of shoe that is recommended for use all the time and by everyone,” says Lewis. “Changing the type of shoes you wear and sometimes going barefoot in the house is probably the best bet so that a range of different leg and foot muscles are used. When it comes to shoes, one size does not fit all.”

Pros and cons of fashionable footwear

Crocs are brightly coloured, rubbery, waterproof clogs. The fit is very wide, so they are good for those who suffer from bunions, but they can cause pain in the Achilles tendon if you are not used to wearing them. Visit crocsfootwear.co.uk for stockists.

MBTs are trainers with a curved sole that promotes instability and encourages a rolling front-to-back action. Studies suggest that they can help to reduce arthritic and back pain but they are not suitable for everyone and could make back pain worse. Because they need to be fitted, they can be purchased only at accredited stockists: see mb-uk.com.

Birkenstocks are the original walking flip-flops and sandals. Their cupped sole offers some support so that the toes are not “clawing” as much as they do in ordinary flip-flops. But they are not designed for long distances, as there is minimal support for the upper foot. See Birkenstock.co.uk for stockists.

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