Why don't boxers' skulls shatter from the forces of punches?

[BioPhysics2021]

Hi All,

My question is in relation to forces that can come through movement. For example, the skull is stated to take around 520 pounds of force or around 2000N:
https://www.virginialeenlaw.com/help/how-much-force-can-a-human-skull-withstand.html

However, boxers can punch well in excess of 2000N of force:
https://bjsm.bmj.com/content/39/10/710

So then, how come boxers who get punched in the head don't have their skulls shattered straight away?

 

[PeroK]

Hi All,

My question is in relation to forces that can come through movement. For example, the skull is stated to take around 520 pounds of force or around 2000N:
https://www.virginialeenlaw.com/help/how-much-force-can-a-human-skull-withstand.html

However, boxers can punch well in excess of 2000N of force:
https://bjsm.bmj.com/content/39/10/710

So then, how come boxers who get punched in the head don't have their skulls shattered straight away?

You are obviously misreading the first article. It talks about pressure and not force.

 

[BioPhysics2021]

You are obviously misreading the first article. It talks about pressure and not force.

Sorry, I don't understand. The text as taken from the article is here:

"His bottom line, primarily based on a bike-helmet study published in the Journal of Neurosurgery: Pediatrics, is that a skull crush would require 520 pounds (2,300 Newtons) of force"

Is this not talking about force? I do appreciate that it also states

"Turns out the human skull can withstand 6.5 GPa of pressure, while oak holds up under 11, concrete 30, aluminum 69 and steel 200."

But I don't see how these are linked.

 

[PeroK]

"His bottom line, primarily based on a bike-helmet study published in the Journal of Neurosurgery: Pediatrics, is that a skull crush would require 520 pounds (2,300 Newtons) of force"

Is this not talking about force? I do appreciate that it also states

That makes no sense, unless you know the area of the helmet involved.

"Turns out the human skull can withstand 6.5 GPa of pressure, while oak holds up under 11, concrete 30, aluminum 69 and steel 200."

But I don't see how these are linked.

That's better. It's ultimately pressure (force per unit area) that determines whether something breaks.

 

[BioPhysics2021]

That makes no sense, unless you know the area of the helmet involved.That's better. It's ultimately pressure (force per unit area) that determines whether something breaks.

Oh, so what you are saying is that whilst 2000N may be generated by a standard boxer, concentrating all of that in a small area is what leads to the fracture/break.

But why does the first statement make no sense?

 

[PeroK]

Oh, so what you are saying is that whilst 2000N may be generated by a standard boxer, concentrating all of that in a small area is what leads to the fracture/break.

But why does the first statement make no sense?

If you step on a nail, there is no more force than if you step on the floor. The nail does damage because the force is concentrated at a point. You could potentially fracture a skull with very little force if you used something sharp enough.

 

[BioPhysics2021]

OK. I understand your answer.So then the summary is as follows:

1) Boxers may be able to generate massive amounts of force however unless this is delivered to an appropriate small area the pressure is likely to be much smaller. For example, if we take the most conservative estimate that the boxer punches in a 1 mm square area with 2000N of force, then the pressure amounts to 2GPa. Given the size and shape of the human hand the area is much more and therefore the pressure is much lower.

 

[PeroK]

OK. I understand your answer.So then the summary is as follows:

1) Boxers may be able to generate massive amounts of force however unless this is delivered to an appropriate small area the pressure is likely to be much smaller. For example, if we take the most conservative estimate that the boxer punches in a 1 mm square area with 2000N of force, then the pressure amounts to 2GPa. Given the size and shape of the human hand the area is much more and therefore the pressure is much lower.

Boxing gloves are quite big. I would guess that the area of impact is more like $20cm^2$. That would give about $1MPa$.

 

[BioPhysics2021]

Sorry, this seems a bit strange.

1 square mm --> 0.000001 square meter.

So then, P = (F/A) = (2000/0.000001) --> 2 000 000 000 Pascals which amounts to 2 GPa. Where did you calculate 2000 GPa from?

 

[PeroK]

Sorry, this seems a bit strange.

1 square mm --> 0.000001 square meter.

So then, P = (F/A) = (2000/0.000001) --> 2 000 000 000 Pascals which amounts to 2 GPa. Where did you calculate 2000 GPa from?

Yes, I got Mega and Giga confused!

 

[BioPhysics2021]

Yes, I got Mega and Giga confused!

OK. Thank you.

Now, as the head is curved would this mean that the force per unit area (i.e - pressure) is smaller or larger upon impact?

 

[PeroK]

OK. Thank you.

Now, as the head is curved would this mean that the force per unit area (i.e - pressure) is smaller or larger upon impact?

Now you are getting into specific experiments to study this. There are many factors relating to the shapes involved and the dynamics of the punch. There must be a whole science now computer modelling contact sports.

 

[Lnewqban]

Note that the first article talks about a skull that is placed against a flat surface or fixed to a support.
In boxing, the head inmediately accelerates; therefore, some of the input energy becomes kinetic energy of the skull.
The shull has not a spherical shape and thickness of the shell possible varies according to the area, because of that there should be weakest and strongest areas.
Note as well that the gloves protect the nuckles and metacarpal bones of the puncher as much as the skin and bones of the receiver, by distributing the force of impact on a larger area (more cross-section of bone is loaded) and by increasing the time lapse of the impact (reducing peak acceleration).

Please, see:
https://en.m.wikipedia.org/wiki/Boxer's_fracture

https://www.forcenecessary.com/boxing-gloves-are-for-boxers/

:)