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I've often heard in various martial arts circles a lot of claims regarding:

  • The amount of force/pressure required to break a knee/ribcage/etc (e.g., the statement that a board is roughly equivalent to the ribs I've heard from multiple sources)
  • The amount of torque required to break a neck

Sometimes the figures I've seen vary enough that I know they can't be coming from the same source.

What I haven't seen is a good study or biomechanical analysis that would back up any specific set of numbers. Is this a well studied problem, and if so where are the studies, or are the numbers simply guesses?

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Good question :) The neck is an interesting one - it is suprisingly hard to break unless you use the exact right angles - then it becomes quite easy. The actual amount of force to break an arbitrary rib would also be influenced by the density of the muscle/fat covering the area. –  slugster Jan 15 '13 at 5:30
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Journal of Trauma may have some accurate numbers there. But not having access, I cannot check it out -- anyone in academia? –  Sardathrion Jan 15 '13 at 8:37
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There was a study done by the Society of Automative Engineers that calculated the force required to break various bones by using cadavers (Vol 4, Biomechanics of Impact Injury and Injury Tolerances of the Head Neck Complex) that provided these equivalences (props to Ronin on the Bullshido forums for sourcing the data):

  • Throat- 300 lbs of force
  • Frontal bone (forehead)- 1900 lbs
  • Back of head (occipital)- 2100 lbs
  • Mandible - 800 lbs
  • "nasal bone" - 200 lbs
  • Cervical vertebra - 500 lbs
  • Crown of head - 1350 lbs
  • sternum with 4" deflection (penetration) - 960 lbs
  • ribs - 400 lbs ( 1-3 ribs are the hardest, 4-9 the most common to fracture)

Doing some really rough math, I came up with roughly 273 lbs of force to break a 1" pine board (rough because I had to convert from a bare minimum break that was calculated rather than measured; should be in the neighborhood regardless). So one board might be equivalent to a weak rib, but you really need 1.5 boards to truly simulate a rib.

So, in all reality, it doesn't take much force to break the neck bones. That said, these bones are extraordinarily cushioned within the body by musculature and cartilage and are mobile enough to absorb more force than raw "force to substance" measurements would indicate.

Which leads to the torque question, which is a fair bit harder. There are a lot of variables there - support of the neck by musculature, technique used to apply torque and the point at which the torque (and resulting pressure) is applied. I can't find any references for this particular question and the more I think about it, I'm not sure there is a set answer. Torque is a measurement of force times distance. In terms of breaking something, you can compensate for a lack of distance by increasing force and vice versa (I'm simplifying somewhat, but the principle is correct).

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