Exercise for low back pain: Why you should stop doing back extensions

Back extensions are popular with people looking to target and rehabilitate their lower back. But if you’re in that position or these have been suggested by your trainer, there are a few reasons you should think twice before giving them a place in your exercise regime. 

In this blog we’ll look at some of the anatomical reasons you should think about your approach to low back rehabilitation differently. We refer to the book, Low Back Disorder by internationally recognised low back specialist, Dr Stuart McGill, and we look at an alternative exercise that could work to help improve your low back pain.

First, some anatomy to help us understand the back muscles at play

When we’re talking about the lower back and lumbar region, we often talk about groups of muscles called extensors, flexors and iliopsoas. These attach to the spine via soft tissues or tendons. And if injured or weakened can cause pain in this tendinous lower back area. 

This time though, we’re going to focus on different muscles, the illiocostalis lumborum and the longissimus thoracis. These are deep back muscles that run the length of the spine and the thoracic region or rib cage, down into the lumbar area.

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How do back extensions work?

Back extensions are specifically designed to train the lower back muscles in order that they hold the spine in a more effective position. They can either be done on a machine using weight resistance or by laying face down on the floor and pushing up onto your arms.

Either way, by isolating and ‘working out’ these muscle groups by doing back extensions, we can often end up doing more harm than good. Back extensions cause us to bend forward and push back creating up to 6,000 newtons of compression around the spine, at best putting unwanted pressure on the lumbar spine and at worst causing disc herniation. 

But apart from this, it’s just not an efficient way to strengthen the back. Better, is to bring those long deep back muscles in to support too.

As Dr McGill says, “…exercises to isolate lumbar muscles cannot be justified anatomically or from a motor control perspective, because all the players in the orchestra must be challenged.”

We need to think differently about strengthening the lower back

So, the goal is to exercise this lower tendinous part of the back in a way that is least likely to cause damage and will offer the most benefit. 

From Dr McGill: “Training the lumbar extension mechanism must involve the extensors that attach to the thoracic vertebrae, whose bulk of contractile fibres lie in the thoracic region because they have the greatest mechanical advantage.”

We need to get those long, vertical muscles involved. 

These muscles are different from the lower back ones though. They are movement muscles like the hamstring, bicep or tricep. They are attached at one end, the lumbar end, to a fixed bone. While higher up they are attached to bones or joints that are able to move.

When these muscles contract they pull on the rib cage from above and then they pull on the tendinous sheath below and thus they hold the lower part of the back and spine, stabilising it most effectively. 

In McGill’s words, “Research shows that the aforementioned muscles that attach to the thoracic region are actually the most efficient lumbar extensions because they have the longest moment arm.”

Think about this in engineering terms

Put simply, a moment arm is the distance between a joint and the force acting on that joint. Imagine you’re using a spanner to undo a nut. The further you hold the spanner up the shaft, the easier it becomes to undo the nut, because you’re exerting more force on it. Hold it lower down and it’s inefficient.

The same goes in the case of your back. If we can train the longer, higher muscles, they are able to work the lumbar muscles and hold the spine in place more efficiently.

If we’re just trying to contract the lower lumbar region by doing back extension exercises, we’re being inefficient. We’re missing out on what these larger muscles should be doing for us. Because we’re not getting them to pull on the tendons, we’re not getting them to pull the area nice and tight. The lumbar extensors are holding the moment arm low down. But if we can get the thoracic extensors going, we’re using a more effective mechanism to contract the area.  

So, if not back extensions, then what?

In order to efficiently exercise and rehabilitate the lower back region it’s important to get multiple muscles working at any one time. 

One exercise that Dr McGill includes in his big three, and I recommend as part of the four fundamental exercises that I give to people who suffer with low back pain, is the Bird Dog.

This exerts only half the newtons of compression on the spine, as you’re only using half of the muscles at any one time. Plus, by raising your arm you’re extending the muscles in the thoracic region which starts to activate the longisimus and the illiocostalis muscles. As we lift the right arm it will stretch the right-hand side of spine. And as you put that one down and lift the other arm it will stretch out the other side. Which works to exercise the back muscles without taking the spine from full flexion to neutral or extension position, aggravating it that much more. 

If you’ve been asked to use back extension machines as part of a fitness routine at your local gym, I would recommend you say you’d rather not. Even the best specialist machinery used in clinics will not offer the most effective way of doing it.

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