Here's a link with formalae for Had Injury Criteria.
http://www.eurailsafe.net/subsites/o...age3.3.1.3.htm
Though I do feel the need to remind you that the calculations you have been doing are based on very loose estimates and that the forces you are dealing with are small. The calculations in the link are used to calculate probability of serious injury.
It may be comforting to work things out (I certainly found it so!) but you must also seek a balance in perspective. Try not to fixate on one element, but explore the variables and subject as a whole. It is good to exercise your brain.
In unrelated research I have been exploring prime sequences and geometry, and sometimes I get an odd warm feeling like a peice of the puzzle slipping into place. Its strangely like the damaged parts/interuped info flow have become like a child that needs to remember what are useually fundamental processes.
PerhaPs our proprioception filters tend to get a bit squiffy under pressure.