Does pain severity or duration measure the severity of injury that is occurring?
It might surprise you that pain severity and injury severity are not as hand-in-hand as you might expect. To give a stimulus that causes musculoskeletal pain (as opposed to psychological causes), the stimulus can be:
- Mechanical: pressure/shear/tension;
- Chemical: inflammation/capsaicin/acid etc; or
- Thermal (cold/heat).
The easiest stimulus to control is thermal. We all know that touching something around 50deg C doesn’t hurt as much as something 100deg. So, the nervous system is doing its job to give us a meaningful warning, telling us to protect from exposure to those temperatures, but it is often not as simple as that.
In research labs, thermodes can precisely control temperature of an electrode the size of a matchbox, which is rested on the skin to test the thresholds and severity of people’s pain perception. With sustained heat, approximately 45deg or more can cause a burn injury. To test the relationship between severity of stimulus and severity of pain, Robert Coghill and colleagues (2013, PNAS) applied a thermode at 49deg C. More than enough to provoke pain in most people. If we rate pain on a 0-10 scale, from 0 = no pain to 10 = worst imaginable pain, with 49deg you might expect most people to rate the pain a perhaps 4-7/10.
When Robert tested 17 people, the pain that they experienced ranged from 1-9/10. Pain is an individual experience. Sometimes the pain that you feel will give far too little or far too much warning relative to the severity of stimulus or injury.
