[QUOTE=Countrywood;7077267]
A vest deflating might allow a fracture or fragment to move or shift, but based on what I have seen of rider behavior after a fall (including my own), the people do their own shifting. Everyone’s instinct is to try to get up, or move a bit to see what hurts etc. Even if someone loses consciousness, the minute they come to, that is their instinct, to move try to get up, etc. Even if they can’t get up they shift this way and that. I have never seen anyone lie rock still after a fall (hopfeull never will as that would mean they were dead)[/QUOTE]
There is actual empiric evidence on this subject when it comes to patients with spine injuries. A conscious, non-concussed person with a spine fracture can pretty much be counted upon not to move in a way that will increase their risk of spinal cord injury. We use this principle all the time in clinical practice. For example, we might have a patient with a C5 fracture without spinal cord injury. Based on the imaging, we may not be able to tell if the fracture is unstable and thus requires operative fixation. If the patient is conscious and not on meds which alter their sensorium, we might send them down for X-rays where we remove their collar and have them flex and extend their neck fully. This is safe only because pain from fracture instability will make the patient stop moving before they cause neurologic damage. So while some people might jump up from a fall, a conscious patient with an unstable spine fracture will not, across all of my experience. Also, unconscious people are not likely to jump around in my experience either 
So, the only scenarios where I worry about movement occurring in a patient with an unstable fracture are when the patient is concussed (have done this one myself) and thus not picking up the cues from their sensory system, or when others move a patient and inflict harm unknowingly. There is an interesting body of knowledge looking at patients with ore existing spinal pathology (ankylosing spondylitis, also other fixed deformities or prior fusions) who have a new traumatic fracture, are neurologically normal, and then get strapped to a back board and become paraplegic. I’ve seen about 15 of those in my career.
Bottom line - if you are thinking clearly and moving of your own volition, your body almost always protects you from making a spinal injury worse.
to speculate, to gush, to use hyperbole, and to say things that we think are reassuring and helpful without considering that these words might be misinterpreted. 
