You would think that space would be a happy place for your back. Actually, it isn’t and let me try to explain why.
Astronauts and their back pains
We have known for quite some time that astronauts often suffer from back pains. Why is that? Recently, a manuscript titled : “Disc herniations in astronauts: What causes them, and what does it tell us about herniation on earth?” published in Europeon Spine Journal looked at why astronauts develop more disc herniations. This narrative literature research review was in response to a 2010 publication in Aviation Space Environment and Medicine whereby they concluded a positive correlation between disc herniations and astronauts.
To get the framework
Over the course of the day, down on Earth, the spine undergoes this accordion height change. When we are vertical and awake with muscle activity, the spine is under compression. This is similar to how a tire of a bicycle, when left long enough will slowly loose its pressure, so does the spine but at a much faster rate. Actually, on Earth we lose up to 2.5 cm in height over the course of the day and this loss is ex-pulsed from the intervertebral discs. The discs are hydrophilic (water-loving) structures that resist compression so our vertebrae do not get too close to one another.
On the other hand, when we lie down (or go to space) the discs swell up to recharge the fluid loss to prepare for more load.
What happens when astronauts travel to space for extended periods of time is something similar to what we experience when we sleep-in longer than usual–an over filling of the discs. Astronauts have to resort to spinal compression exercises in space to prevent the discs from over swelling but the astronaut compliance is low because the strapping down exercises are uncomfortable to do.
When the discs are over inflated, and are subjected to flexion loads, they are more susceptible to herniations through annular fissures. This can be seen in a spine model specifically designed to demonstrate this. This has been years in development. You can see the product here.
So what can we learn about this research?
It is important to keep the discs balanced with regard to compression and decompression. If discs are over-inflated, they are susceptible to disc herniation injury. On the other hand, if the discs are under-inflated, other problems can develop like degenerated disc disease. Most people fall into the latter category and require more off-loading and this is why I took the time to publish a simple unloading strategy for the lumbar spine called chair-care.