If you don’t like spending time crunching your abs then we might have some good news. Researchers are not only arguing over whether sit-ups do you any good – but whether they might even be bad for you.  

Do they give you a taut six-pack across your abdomen or does a flat stomach depend more on diet and general exercise than a specific routine? A review of all the research conducted on sit-ups reports evidence that they do improve flexibility and muscle strength and that in dogs flexing the spine has been shown to help the delivery of nutrients to the discs which could prevent stiffness.

So far, so good. But to get the desired six-pack does take an awful lot of work. In a small randomised controlled trial in Illinois in 2011 one group did daily abdominal exercises while the lucky control group did none. After six weeks detailed measurements were taken and it was found that the sit-ups made no difference to waist size or the amount of fat around their stomachs.

Many sportspeople do sit-ups as part of a raft of exercises which aim to improve their core stability, but research from Thomas Nesser from Indiana State University suggests that improving your core stability doesn’t necessarily result in better athletic performance.

Whether or not they provide you with precisely the physique or fitness you desire, could sit-ups bring unintended consequences such as back pain? Stuart McGill, professor of spine biomechanics at the University of Waterloo in Canada has been studying sit-ups for years and is convinced that the traditional crunch does indeed cause us harm.   

Research published in 2005 on soldiers stationed at the US military’s Fort Bragg attributed 56% of all the injuries sustained during the two-yearly Army Physical Fitness Test to sit-ups

He conducted dozens of studies in his spine biomechanics lab using the cadavers of pigs, repeatedly flexing their spines in a similar way as a person might when doing a sit-up, but for many, many hours at a time. When he examined the discs in the spine afterwards, he found that they had been squeezed to the point where they bulged. If the same thing happened in a human this would press on the nerves, causing back pain, and possibly even a herniated disc.

Pigs were chosen for this experiment because their spines are more similar to human spines than those of many other animals, but of course critics of these studies point out, that there are still many differences between people and pigs. Also these studies involved thousands of continuous cycles of bending. Even when training hard, people take breaks between sets of crunches.

Perhaps these results tell us what might happen at the extremes in the unlikely event that you were to do sit-ups for hour upon hour, but in real life it’s clearly not the case that most people damage their discs most of the time when doing sets of 15 sit-ups. However, injuries can happen. Research published in 2005 on soldiers stationed at the US military’s Fort Bragg attributed 56% of all the injuries sustained during the two-yearly Army Physical Fitness Test, to sit-ups.

Some people seem to be more prone to back problems caused by sit-ups than others. We might be fine doing 30 sit-ups a day for decades, but we might not and it’s hard to know which group we fall into. It could come down to our genes. According to one paper, it’s not wear-and-tear that causes most of the difficulties, but genetic factors, which account for three-quarters of the differences between the people who do get back problems and those who don’t.

But if you want to crunch those abs, is there a way of limiting the risk?

The Twin Spine study has been following pairs of twins in Finland, Canada and US since 1991. The researchers have found that genetics play a huge part in people’s susceptibility to the degeneration of the discs in their backs. Even when one twin had a job requiring heavy lifting, while the other had a sedentary job, the frequency of back problems was about the same.

So sit-ups might lead to back pain, but only in some people. It’s a good excuse not to do them. But if you want to crunch those abs, is there a way of limiting the risk? Professor Stuart McGill recommends sliding your hands under your lower back to stop it flattening against the floor. This minimises the stress on your back. Bend one knee up and keep the other extended. Then raise the head and shoulders off the ground by a very small amount. He says to imagine your head is resting on bathroom scales and you are just lifting your head enough for the scale to show zero. This exercise is described in much more detail in his book Back Mechanic.

In his review of the sit-up research Bret Contreras from Auckland University of Technology in New Zealand recommends limiting spinal exercises to 60 repetitions per session, beginning with only 15 and building up gradually. Finally, when we’ve been lying down overnight or even sitting down for a long time we gain a small amount of height, which makes sit-ups harder and increases the risk of injury. So don’t stand up from hours of sitting at your desk and immediately get down on the floor to do sit-ups and don’t bound out of bed and do them first thing in the morning.

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