We’ve all heard that correct deadlift form involves keeping your back straight. We’ve seen that guy in the gym pulling way too much weight off the floor with his knees practically straight and his spine a perfect semi-circle. You know the feeling of watching him, cringing, expecting that spinal disc to pop at any moment. This can’t end well.

But hang on a minute – we’ve also seen powerlifters lifting incredible amounts of weight, without being anywhere close to spinal neutral. If anyone knows anything about lifting heavy weights, it should be them. So what gives? Is lifting with a rounded back as bad as we’ve been led to believe? Is it an injury waiting to happen or a lot of fuss about nothing?

What’s the evidence that spinal flexion is bad?

It might be helpful at this point to quickly review a bit of spinal anatomy. Your spine is a string of bones on top of each other, and in between each pair of bones there are two joints (one on each side) and an intervertebral disc. These discs consist of a fibrous outer layer, with some squidgy stuff in the middle, a little bit like a jam doughnut. A prolapsed (or “slipped”) disc occurs when the fibrous outer layer of the disc is damaged, and the squidgy stuff leaks out, sometimes putting pressure on the nerves and causing both back and leg pain. Prolapsed discs are by no means the only cause of back pain, or even a particularly common one. In fact, it turns out that many prolapsed discs are asymptomatic, and are far more common than we used to think. However, they can be particularly unpleasant and are something that you probably want to avoid if possible.

Whenever we move or lift something, we apply a load to the spine. How this load is distributed and the effect it has depends on the position that the spine is in. Some research (much of it involving dissected pig spines) has suggested that the intervertebral discs are particularly vulnerable to injury when the spine is flexed (rounded) under load. When the spine is loaded in the mid-range of its movement—the neutral zone—the discs are much less likely to be damaged. There are also some biomechanical models that suggest that the shear forces acting on the spine may be more problematic in flexion. This has led to the widespread advice to avoid flexing the spine, with some even suggesting that any flexion at all is bad and will inevitably result in injury sooner or later.

So why don’t powerlifters’ spines explode?

First things first: not all rounded backs are the same. If you look carefully at what powerlifters are doing, they usually begin the lift with their back rounded but braced. In other words, their spine is in a flexed position, but static. This is different from moving dynamically into flexion while under load. They are also not at the extreme end-range of flexion, but somewhere in the middle. Many lifting coaches also advise that the flexion should be coming from the upper back, and that lower back flexion should be avoided. These distinctions all change the mechanics of what is going on; your experienced powerlifter is not doing the same thing as that novice in the gym who’s just chucked way too much weight on the bar. Less experienced lifters may have a harder time spotting the difference, much less imitating it, which is an excellent reason to start by learning to deadlift with the spine in neutral.

Next, a dissected pig spine doesn’t behave exactly the same way as yours does. Importantly, your spine has muscles attached to it that affect how it moves under load, and unlike the unfortunate dead pig, your spine also has the ability to adapt based on the forces that it’s exposed to. This is one of the key principles of training: if you gradually expose your body to certain loads (in the absence of injury), it will adapt to become better at handling those loads. This applies not only to muscle but also to bone, connective tissue, and spinal discs. We know that bones and connective tissue (found in ligaments, tendons and spinal discs) adapt to the specific stresses put on them; if loading in flexion is applied consistently and progressed gradually enough then the spine should—in principle—become stronger in this position. This sounds like good news, but bear in mind that we don’t yet have a lot of data about the extent to which this process of adaptation can protect the spine, or how much it varies from one person to another.

It’s also important to remember that the discs aren’t the only parts of the spine that can be damaged. In fact, it’s thought that a relatively small percentage of back pain can be directly attributed to disc damage. There’s some evidence that other structures might be damaged just as easily—perhaps more so—in a neutral position. What’s more, in many cases of back pain, it’s impossible to identify any damaged structures at all. Back pain turns out to be a whole lot more complicated than the dissected pig spine might suggest.

After all that, it turns out that we may not be able to avoid loaded spinal flexion anyway. It’s involved in a lot of sport specific movements, and even with gym exercises that are taught with a neutral spine, biomechanical analysis suggests that this doesn’t happen in practice.

Finally, there’s the trade-off between risk and benefit to consider. Despite the fact that lifting with a rounded back may not be as dangerous as we’ve been led to believe, most lifting coaches acknowledge that keeping a neutral spine is (probably) safer, and recommend that people start by learning to lift in this way. However, if your objective is to lift as much weight as you possibly can, then for some people (depending on lifting technique and body type), using a flexed spine may help you to hit that personal best, even if that comes at a (somewhat) increased risk of injury. If on the other hand, you just want to lift weights to get stronger, then it may be that you’re better off staying in neutral.

The verdict: Probably TRUE under certain circumstances, but the evidence still leaves a lot of room for uncertainty, and there are a lot of unanswered questions.

Some rounding of the back is probably inevitable with most sporting and weightlifting activities. A sensible compromise would involve being cautious with flexion under load (and especially when moving into flexion repeatedly under load), but not to try and eliminate flexion altogether. Since muscle, bones, and tendons all adapt to the specific loads put on them, training your back muscles to function effectively in a flexed position may even be protective for the back, providing it is done carefully and progressed very gradually. The limits of how much flexion can be tolerated, and to what extent it may be beneficial to the back, are poorly understood, and will no doubt vary from person to person.

Of course, if you already have a back condition that’s aggravated by forward bending then it makes sense to avoid flexion, at least while it recovers. (Many physiotherapists do advocate reintroducing flexion later in the rehabilitation process.) For most people, though, there’s probably no need to worry too much about bending forwards during normal everyday activities, such as tying your shoelaces or picking up something light.