From Bullshido :

http://www.bullshido.net/forums/showthread.php?t=5903

Here are some listings compiled by user BatRonin:

"There has been some talk lately of how tough ot how weak the human body is.
There have been studies done on this by the SAE ( Society of Automotive Engineers).
There have been also many studies done on how much force a boxer ( for example) can hit with.
The latest:
By King at Wayne University:
Boxers can hit with an average force of 765 lbs
so, let us take that as an example and see what the bosy can with stand:
Biomechanical injury tolerance levels:
Throat- 300 lbs of force
Frontal bone ( forehaed)- 1900 lbs
Back of head ( occiptal)- 2100 lbs
Temporal - 1400 lbs
Zygomatic-800 lbs
mandible - 800 lbs
maxilla - 500 lbs
Lat. Maxilla - 700 lbs
"nasal bone"- 200 lbs
Cervical vertebra - 500 lbs
Crown of head - 1350 lbs
area above the ear - 650 lbs
sternum with 4" defelction ( penetration) - 960 lbs
ribs - 400 lbs ( 1-3 ribs are the hardest, 4-9 the most common to fracture)
Draw you own conclusions"

"The study was done on amateures and pro's, not much of a diffrence in punching power, although alot of difference in terms of stamina ( makes sense).
As for the rating, force when applied to impact is measured as peak force of lbs or Newtons, it is not meaured per sq inch or such, that applies to pressure, not impact.
It can also be meaured in J or Joules, I t converted them all to lbs to make it easier.
The boxers weighed in at various weights of course, the hightest values found were those who had the best combination of size and speed.
I believe the highest was actually 1200lbs and the boxer weighed 180lbs.
As for where you canget this info:
Society of Automotive Engineers (SAE)
4 vol, about 300 us each.
Biomechanics of impact injury and injury tolerances."

"The values were taken by doing impact studies on cadavers.
The values usually used are from the cadavers the repesent 75% of the population, the values I took are from the 10% percentile study, males over 5-11 and over 200lbs.
They are the upper values taken, which means that in 100% of the cases when the force valued reach the amount stated, a fracture accured, a fracture that would be considered traumatic."
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