Injury is a process – not an event
I often hear people describe their back injury as a minor movement like picking up a pencil off the floor or ‘turning the wrong way’. Sound familiar? It’s happened to me more than once. The reason for this is simple:
A back injury is a process, not an event.
In many cases, a back injury is a result of a combination of activities that you were doing before your injury. The graphs below give a good illustration on how the tissue fails from repetitive movements or static loading. I’ve replicated these from McGill – Journal of Biomechanics.
Repetitive Load
The first graph shows us that repetitive loading without the proper work/rest ratio will eventually lead to injury, or ’tissue failure’, as the researchers call it.
Example: A warehouse worker handling boxes of product. When an item is lifted and then set down, the spine experiences a cycle of high load followed by no load (ie. picking up the item, then setting it down). At the start of the shift, there is a large gap between tissue tolerance (red line) and the load (green line). As the cycle continues, the ability of the tissue to tolerate the load gradually reduces. Without the proper work-rest ratio, the tissue is unable to stabilize the spine and eventually fails (purple star), resulting in an injury.
Purple star = Injury = Bad
Sustained Load
The second graph shows us how static loading (ex. prolonged forward bending) can also lead to tissue failure.
Example: A mechanic working on an engine when bending forward for long periods. In this case, the load on the spine is constant but eventually this can stretch out ligaments and destabilize our spine, which results in tissue failure to the spine (purple star). Without the proper rest, the spine eventually fatigues and is not able to stabilize itself.
Keep in mind that an injury can occur while performing an activity, but may also occur shortly afterwards if the spine hasn’t fully recovered from the previous tasks (loading or bending). This is why a relatively small movement like twisting to talk to someone or picking up a pencil off the floor can result in injury. The spine is already susceptible from what you were doing before and this small movement was the ‘straw that broke the camel’s back’ (no pun intended).
Purple star = Injury = Bad
Ideal
The last graph shows the ideal scenario for preventing tissue failure. Alternating tasks, mixing up the work and taking microbreaks will allow the spine to recover and prevent injury.
NO Purple star = No Injury = Good
Do all jobs allow this nice variation of work? Nope. Sometimes, the nature of the work, environment, pace, etc will dictate how you load and position your spine. You can’t achieve this all the time, but there are some things you can do during a microbreak to minimize the risk of injury. Have a look at the following blog posts to check out how the tissue ‘fails’ and what you can do about it.