With over 600 million people affected, lower back pain is one of the common reasons people miss work. But why are so many people crippled by this injury? Recent research suggests that the endurance of our back muscles may be one of the leading causes. ‘Having less back muscle endurance was probably rare for most humans throughout most of human evolution, until the Industrial Revolution brought increased sedentariness and subsistence strategies other than hunting and gathering and subsistence farming became more common’, explains Benjamin Sibson, a research fellow at Beth Israel Deaconess Medical Center, USA. So, sitting in our office chairs may be making things worse for us with regards to lower back pain, as this doesn't build the endurance in our lower back muscles that we need to support our upper bodies. But do our fatigued lower back muscles also change the way we walk? Sibson, along with Andrew Yegian, Ali Yawar and Daniel Lieberman of Harvard University, USA, looked to see whether having fatigued back muscles would change the posture of some human volunteers when they walked.
When the 12 volunteers showed up to the lab, the researchers first asked them to lie on their stomach on a table with their upper body over the edge while their forearms rested on a chair in front of them. After the team strapped the participant's lower body to the table, they asked the participants to cross their arms over their chest and hold their upper body straight for as long as they could. This let the researchers find out which of the participants had back muscles that got tired quickly and which had more endurance. After this, the researchers videoed the participants while walking on a treadmill to see whether the spine was tilting forward, to the sides or twisting. Surprisingly, Sibson and colleagues found that some volunteers had more force on their spine when walking on the treadmill after their back muscles were fatigued. This suggested that their fatigued back muscles were struggling to keep their posture upright as they walked. Were the back muscles really to blame for not keeping them upright?
At the same time as the volunteers were walking on the treadmill, the scientists measured the activity of their lower back muscles and their abs. After their back muscles were exhausted, the participants that had less endurance to start with had more muscle activity in their abs, while those with better endurance had higher muscle activity in their lower back. This increase in ab activity is probably to help stabilize the body during walking because the back muscles are too exhausted. But what would happen if the researchers made walking even more demanding on the abs and lower back muscles? Interestingly, when the researchers added a weighted backpack to the participants, it stopped the spine from moving as much while the volunteers were walking, even when their back muscles were exhausted.
So, what does this mean for the future of back pain prevention? ‘Back pain is a very common condition, and oftentimes (but not always!) people report having “thrown their back out” doing something relatively ordinary, such as bending over to tie their shoes or just coughing’, says Sibson. He goes on to explain that ‘the positive outlook here is that giving attention to developing and maintaining higher back muscle endurance might help prevent these sorts of tweaks, injuries and resulting pain from occurring. Back muscle endurance can be developed and maintained by practicing various light-moderate forms of physical activity like walking’. So to prevent back pain, we should all get back to our pre-industrial roots, or just start taking more walks.
