Engage your core” is a workout instruction that rivals “warm up” and “cool down” for the frequency with which it is issued by trainers. Most of us know that our core muscles wrap around our midriff like a corset and that they are something of a work-out panacea in their ability to improve everything from posture and back pain to stomach flatness.

The principles of core-stability training are the basis of thousands of workouts. Pilates, aerobics classes, running and swimming are only a few of the activities with techniques to improve abdominal strength at ... well, their core.

Core-stability exercise is endorsed by everyone from celebrities to physiotherapists, so there has never been cause to question its wisdom. But the beginnings of a backlash have started to appear. A paper published recently in the British Journal of Sports Medicine suggests that the benefits of core-stability workouts have been wildly overplayed. Professor Garry Allison, of the school of physiotherapy at the Curtin University of Technology in Perth, Western Australia, and Sue Morris, a physiotherapy researcher at the University of Western Australia, claim that when it comes to proof that core-stability workouts are helpful the “evidence is just not there”.

They cast doubt on the notion that back pain is linked to “less than optimal core stability” and suggest that it is linked to poor trunk rotation and strength instead. What is more, the researchers say, the teaching of some core stability moves to people with or without back pain “is at best controversial” since their own review of evidence has shown that the exercises have little beneficial effect. Since core stability became a mantra among fitness professionals ten years ago proponents have believed that a set of muscles in the trunk and pelvic floor work together to protect the spine and keep it stable.

A study at the University of Queensland was the first to highlight the concept, when a team of physiotherapists discovered that people with lower back pain used the transversus abdominis, a deeply embedded muscle that wraps around the lower trunk, when they were asked to perform various physical tests. By learning to engage, or “draw in”, this muscle the subjects found that their back pain decreased.

Experts assumed that a stable core provided people with a strong foundation from which their limbs could move freely and efficiently.

These days core-stability work is implemented in training sessions for everyone from professional foot-ballers to ballet dancers, and as a treatment for back pain sufferers and people who slouch. By pulling navel to spine (a practice called hollowing or drawing in), the aim of these often subtle moves is to switch on the core muscles that, unlike larger muscle groups, may otherwise remain inactive - some trainers describe them as inherently lazy muscles - during exercise. Used often enough,it is thought, the transversus abdominis and other core muscles will eventually work on their own.

However, even the woman who led the Australian study, and who is responsible for coining the term “core stability”, has expressed reservations about its usefulness. Professor Carolyn Richardson, of the Department of Physiotherapy at the University of Queensland, says: “I have found that for the fitness industry it is often a poor instruction that is often misinterpreted or carried out badly. It's easily done incorrectly by people holding their breath or rounding their backs because they are sucking in their muscles so far.”

Indeed, some researchers believe that attempts to strengthen the transversus abdominis through exercise can backfire, with disastrous consequences. In research conducted two years ago Dr Stuart McGill, a professor of spine biomechanics at the University of Waterloo in Ontario, discovered that the muscle does not play as pivotal a role in protecting the back as is commonly thought.

McGill suggests that efforts to strengthen the transversus abdominis could even make back pain worse. After measuring how different loads and weights affected his subjects' spine function, McGill demonstrated that engaging the muscle could weaken the back.

“If you hollow in your muscles as you are instructed in these exercises, you bring the muscles much closer to the spine and you effectively reduce the stability of the back,” he says. “Try it yourself by getting out of a chair with a hollowed out stomach. Not only are you weak and wobbly, it is very difficult.”

Sammy Margo, a spokeswoman for the Chartered Society of Physiotherapy (CSP), believes that core strength is fundamental to a strong, well-functioning body. But it is not without its limitations. “Core stability has become the solution to world peace in the fitness arena,” she says, “but it needs to be kept in context. It can be a factor in treating back pain and posture problems, but it is not a solution.” Margo sees a constant stream of patients with back pain who claim to have been doing Pilates and core-strength work for years. “I would say that 75 per cent of people who do these exercises don't do them properly,” she says.

Claire Small, also from the CSP, says that incorrect technique can worsen existing back pain. “What should happen when you engage the core muscles is that the abdominal and pelvic muscles inflate simultaneously like a balloon inside the abdominal cavity,” she says.

“Bad technique can cause the pelvic muscles to drop, which is potentially weakening for the back. Ligaments can tighten if people mistakenly restrict their breathing or flex their spine while doing the moves and all of this can cause the back pain that this sort of exercise is meant to avoid.”

Margo says that we should take an holistic approach to core training. “It should not be about a few exercises done lying on the floor,” she says. “You need to address your lifestyle, stress levels, fitness and diet. It's not enough to do a few core-stability classes and think you will be OK.”

How to strengthen your core

Brace yourself Dr Stuart McGill, a professor of spine biomechanics at the University of Waterloo, Ontario, says that when you lift something or exercise, rather than pulling in from navel to spine you should brace all the abdominal muscles. “Bracing is stiffening the abdominal wall,” he says. Imagine that you are going to be hit in the stomach. The instinctive reaction is “bracing”.

Middle way Professor Carolyn Richardson, of the University of Queensland, says that instead of trying to contract the core muscles during a workout, people without back pain should strengthen the middle area and protect their back by stretching tall through the back of their head and relaxing their shoulders.

Times recommends

• Tewkesbury: when the memories flood back
• How I lost the gift of joy for a while
• The A-Z of winter style rules