It is favoured by celebrities and athletes alike, and widely considered the best form of exercise for improving back pain and poor posture. But some spinal experts are casting doubt over the ability of core stability training - the bedrock of fashionable fitness activities such as Pilates - to relieve back problems, suggesting that many who take it up do themselves more harm than good.
Contrary to claims often made by the fitness industry, research has shown that workouts claiming to strengthen the deeply embedded "core" muscles in the body's abdominal area are not necessarily helpful, often worsening pain. Earlier this year, a paper published in the British Journal of Sports Medicine suggested that the benefits of core-strength training have been grossly exaggerated. Professor Gary Allison of the school of physiotherapy at the Curtin University of Technology in Western Australia tried to find proof that such exercise helps prevent or treat back pain and concluded the "evidence is just not there". He and his team cast doubt on the link between back pain and a lack of core strength, suggesting that published findings fail to produce any substantiated benefits for core stability training exercises.
Other researchers suspect the advantages of core strength training have been overplayed. Stuart McGill, a professor of spine biomechanics and the chairman of the kinesiology department at the University of Waterloo in Ontario, says the concept of "drawing in" the deep transversus abdominus muscle by pulling navel to spine and lifting the pelvic floor - a move central to Pilates teaching - is attracting criticism in the medical world.
Popular thinking suggests that when the transversus abdominus muscle is engaged, the torso temporarily acts like a corset, protecting the lower back and that, if the muscle is used often enough, it will eventually fire on its own. But by measuring spinal loading forces and their effects on postural stability, McGill found that the transversus abdominus muscle does not play as pivotal a role in protecting the back as was once thought. "Core stability" first became a fitness mantra 10 years ago when Australian researchers at the University of Queensland's department of physiotherapy revealed that engagement of the transversus abdominus was delayed in people with lower back pain when they attempted various physical tasks. At the time, Professor Carolyn Richardson and her team recommended a treatment approach for physiotherapists that taught patients how to contract both that muscle and the multifidus in the lower back. As well as treating people with chronic back problems, the principle has been implemented in everything from jogging technique to yoga and football training. By far the most popular core-stability training technique is Pilates, named after its founder, Joseph Pilates, a German-born sportsman who devised the exercise method 75 years ago to improve his strength. It is estimated that around 40 million people worldwide now practice the exercise form, in which participants are taught how to target the transversus abdominus muscle. Celebrity fans including Madonna, Sigourney Weaver and Elizabeth Hurley are proof, perhaps, of its promise to help devotees stay toned and slim with good posture. But Professor Richardson recently admitted she was concerned that the fitness industry has made the core stability techniques as popular as stretching and warming up. Applied wrongly or with poor technique, she says, the results can backfire. "Engaging the core and strengthening core stability are not a very well interpreted maxims by personal trainers and the fitness industry," she says. "It is easy to do wrongly and a common mistake is for people to hold their breath or suck in so far that they round and arch their back, which causes problems as the correct muscles aren't being targeted." Even if core stability moves are performed perfectly, some doubt whether they are helpful to bad backs. Professor Shirley Sahrmann, a physical therapist at the Washington University School of Medicine found that, no matter how many times the movement is repeated, it does not become second nature and therefore will not provide constant back support. "I haven't come across a single study that shows 'drawing in' or engaging the core muscles becomes a subconscious reflex," Sahrmann says. "If that is the case I don't see how it can provide the back support it is supposed to." Claire Small, a spokeswoman for the Chartered Society of Physiotherapy in the UK, says that she has seen patients whose back conditions have deteriorated despite their diligently attending Pilates classes or incorporating core strength training into their workouts. "When people engage their core, there should be a simultaneous contraction between the transversus abdominus, multifidus pelvic floor and diaphragm muscles so that they inflate like a balloon inside the abdominal cavity," she says. "But too often, they don't do that and a bad technique will eventually cause the pelvic muscles to drop, which is bad news for people with back pain." Neither Small nor Sammy Margo, also a spokesperson for the Chartered Society of Physiotherapy, dismiss Pilates or core strength training as useless. "It has its limitations, but physiotherapists who know how to teach the techniques safely still use it a lot with their patients," Margo says. "It is one aspect of treatment that can be used for back pain, but it is not a solution. It won't cure it." Indeed, studies have shown that, over time, correctly administered Pilates helps to create a solid cylinder of muscle around the central spine, preventing damaging forces from being applied to the vertebrae, ligaments and discs. A study from the physiotherapy department at Queensland University showed it could reduce back pain. "Improving your core strength can help you to develop a strong back, but should not be a first line of treatment for chronic back pain," Small says. "And you must always seek professional advice before trying to do it."