Ever since Joseph Pilates invented this popular form of exercise, Pilates has been patronized by many including Hollywood celebrities. It is widely recommended for losing weight, reducing or eliminating back pain and improving posture. Yet experts now question whether Pilates is any good, at least for reducing back pain, a common problem in many.
Participants of Pilates are taught to strengthen a muscle called transversus abdominus, which is done by drawing the navel to the spine and lifting the pelvic floor.
Yet, according to Stuart McGill, a professor of spine biomechanics at the University of Waterloo in Ontario, it is this concept of "drawing in" that is the problem.
He and his colleagues have found that strengthening this "core" muscle often worsens back pain.
It was by measuring how different loads and forces affect the way the spine functions, that McGill found that the transversus abdominus muscle does not play as pivotal a role in protecting the back as was once thought.
"If you hollow in, you bring the muscles closer to the spine and you reduce the stability of the back," McGill says. "Try rising from a chair with a hollowed-out stomach. Not only are you weak, it is very difficult."
This 'drawing in of core muscles' became a fitness mantra ten years ago when Australian researchers found that people with lower back pain used the muscle less when they did various physical tasks.
The researchers recommended that physiotherapists teach patients how to contract both the transversus abdominus muscle and another; the multifidus, in the lower back.
Lead researcher, Professor Carolyn Richardson of the University of Queensland's department of physiotherapy, has recently admitted she was concerned that the fitness industry had made the technique as popular as conventional stretching and warming-up exercises.
"I've found that for the fitness industry, it's a poor instruction that is often misinterpreted or carried out badly," she says.
"It is easily done incorrectly by people mistakenly holding their breath or sucking in so far that they round their back."
As a result, the correct muscles are not targeted and, over time, the back becomes more vulnerable than before.
Claire Small, a spokesperson for the Chartered Society of Physiotherapy, echoes her concerns.
"In some people, attempting to engage the core muscles can trigger a reaction that makes their condition deteriorate," she says.
"In theory, all the core, abdominal and pelvic muscles should contract simultaneously so that they inflate like a balloon inside the abdominal cavity, but incorrect technique can cause the pelvic muscles to descend which is bad news as it is potentially weakening for the back."
Yet try telling this to cyclist Jenny Kingsley who broke her hip and suffered constant back pain. She went in for Pilates at the recommendation of her doctor and physiotherapist.
Kingsley had always written off Pilates as a New Age gimmick or an excuse for those who were pretending to exercise.
Not anymore. In her words: "The goal is to strengthen the core or "powerhouse" of your body, the area between the lower ribs and hips. The theory is that a strong centre supports and decompresses the spine, so posture improves. The emphasis is on stretching. The range of movement determines the intensity of the exercise. So you may do small circles with your legs for the first few months and wider circles once you are stronger and can keep your back and pelvis in the correct alignment.
Once your body is no longer scrunched up, your insides function more effectively. The breathing technique helps you breathe fully and wakes up your mind and body. For me, there is gain without pain and, because Pilates makes me feel so good inside and out, I keep coming back for more. My tummy is flatter, I feel suppler, I instinctively sit up straight at my desk and back pain is less irksome."