By Liam Mannix

For ages, bad posture has been assumed to cause back pain. Now some physiotherapists are rethinking what we should be doing with our spines

On the first day of classes at physiotherapy school, all students are made to strip down to their underwear. It’s not a hazing ritual, but it is an initiation of sorts. Unclothed, the students are told to study each other. Who slouches? Who has a flat back? Who suffers from forward head position?

Posture, students are taught, is the key to good health and a strong back. It will be their job, when they graduate, to correct it. People with back pain, they are told, tend to have weak muscles in their backs, leaving their spines vulnerable. Get the postural muscles strong and you could cure the back pain.

Twenty-three years ago, a young Peter O’Sullivan was standing in that line. He remembers copping it from his instructor: he slouched horribly. “Stand up straight, man.” O’Sullivan was the wrong person to target. He remembers standing there, shivering, as his classmates ate up their teacher’s wisdom about bad posture, thinking: “Says who?”

O’Sullivan’s career would be devoted to answering that question. Who says there’s such a thing as bad posture? Where’s the evidence? He pestered his lecturers. He hunted through research papers.

“And I couldn’t find anything,” he tells me. But the accepted wisdom was what it was, and a young physio wasn’t in a position to change the world – yet. Anyway, first he had to fix his own back.

First, O’Sullivan led a team of researchers who conducted a proper, formal search for evidence that posture made a difference to back pain or general health. They found none. Then they started doing their own studies. First they studied people’s postures when they sat, looking at whether they slumped or not. They found no association between sitting posture and back pain. “There’s this kind of fear: ‘My God, if you slouch, you’re going to end up with pain, you’ll end up hunched over.’”

“There is just no good evidence” that posture is in any way a problem, O’Sullivan says. “Often, this is a distractor from the big game. Our spinal health is linked to our general health. Keeping fit and strong. Moving. Eating well. Sleeping well. They’re the things we should be targeting, rather than this idea of targeting body posture. The interventions that have targeted posture haven’t worked. We have to look beyond that.”

O’Sullivan’s ideas troubled me at first because they were so radical. How could posture not matter? But he enjoys widespread support from leaders in pain science. “He’s a very much respected person in the pain space. He’s done an enormous amount of work,” says Tim Austin, chair of the Australian Physiotherapy Association’s National Pain Group. “Peter is on the mark.”

Your posture is governed by the slow-twitch muscle fibres that run through your back. They’re designed to hold positions for a long period of time, but eventually become fatigued. Under stress, they tend to get short and tight. People who don’t move around much tend to overuse these muscles and underuse their more athletic fast-twitch muscles.

What posture should we hold them in? Straight, you might think. But this seems an odd idea, given the spine is naturally curved like an S. Mechanically, it’s just not designed to be straight, says sports and exercise physiotherapist Andrew Smythe. If all the vertebrae were stacked neatly atop one another, there would be tremendous pressure in the bottom components. The S shape is like a suspension bridge, holding thousands of cars aloft by a gossamer thread: it evenly distributes the load across the spine.

“But the precise S-curve of your spine is individual to you. It’s in your genes,” says O’Sullivan. “It’s like our signature. It’s just how we are. This idea of homogenising us, I think it’s more social.”

So where does it come from? The historian Sander Gilman thinks it comes out of the military: the military pose of “standing at attention”, spine rigid, chin tucked, feet under head. This was originally developed as the ideal pose for reloading a musket, and was never natural. Soldiers have to practise it again and again to master it. Over time, this posture became imbued with manliness and honour, and non-soldiers started trying to imitate it. Now we’re all trying to stand to attention.

In a study of 1,108 Australian teenagers using photographic analysis of sitting posture, researchers could find no association between posture and the incidence of headache or neck pain. In adults, there is some evidence of an association between forward head position and neck pain – but it’s not clear which way causation runs. Do we maintain a forward head position because we’re in pain, or does the position cause the pain?

What about back pain? Again, despite dozens of studies, no strong evidence has emerged for a link between posture and back pain, according to an umbrella review of the evidence. Even in people who are forced to take on awkward postures for work, there is no evidence this increases the risk of back pain.

Part of the issue is scientific. “It’s really difficult to measure the different types of physical loads that are placed on the spine. Even changing your posture a little bit can change how the loads are distributed quite a lot,” says Dr Chris Swain, the University of Melbourne researcher who led the meta-analysis.

So we can’t precisely measure the effect of posture on back pain. But, says Swain, there are now enough studies coming to similar conclusions that we can come to an imprecise conclusion: posture likely doesn’t matter, and if it does matter, the effect is very small. “The association just isn’t that strong.”

Compare it with things that really make a difference, like depression and anxiety, and the evidence suggests posture just isn’t worth worrying about for most people, he says. “I’m fairly slouched now – and I don’t worry about it.”

There is some evidence people with chronic back pain have weak back muscles. When you image them, you can see the muscle has become withered and infiltrated by strands of white fat. It’s not clear yet why this is. But it doesn’t seem crucial to back pain, because when doctors devised special training programs to strengthen those muscles they found they didn’t help anyone’s back pain.

“At an undergrad physio level, they talk about ideal posture and biomechanics,” Smythe tells me. Then, after really getting to grips with the research, “you kind of see it’s all bullshit”. If you’re healthy, posture just does not seem to matter that much. “It’s the same with running. Look at some of the best runners in the world – they have really funky techniques that don’t fit the textbook, but structurally and functionally they’re strong,” says Smythe.

Of course, there’s no evidence sitting up straight is actually bad for you, experts said. If you feel comfortable that way, or think you look better, go for it.

There’s one area where posture does seem to make a difference: movement. But it’s not the posture we hold, it’s the movement between postures.

After panicked headlines (inaccurately) proclaiming sitting was the “new smoking”, modern offices have embraced sit-stand desks. But Smythe and his colleagues aren’t seeing any fewer injuries. Standing in a static position places as much stress on the body as sitting in one.

In several studies, researchers have found a link between people who don’t move much between different sitting postures over the course of a day and back pain. The idea seems to be that there is no one ideal posture, but that our bodies do best when they’re regularly moving between different postures, straining and working different muscles.

Indeed, this is probably why we get sore if we sit the same way for too long: not because we’re damaging our backs, but because our pain system is telling us to move, please.