# Force of a full body jerk (myoclonic jerk)

1. Feb 23, 2015

### freexd

Hi there,

I would like to know how much force a full body jerk creates. You've probably all experienced this, when you were just about to sleep in, when suddenly your whole body jerks.

I know that it is probably very difficult to measure the force excactly. But what might be the probable range?

2. Feb 23, 2015

### A.T.

Force where exactly? You can look up at the maximal forces that muscles can produce, to get an idea of an upper limit. But it's difficult to measure those forces in vivo during a seizure. EMG can give you a rough estimate if well calibrated.

3. Feb 23, 2015

### freexd

Yes, of course the first question must be which muscels are even involved. And secondly their maximum force is decisive.

I would say, from my experience that in most cases the muscles of the back and neck are primarily involved. I found the info that jerks are about 10-20% of the muscles maximum force.

You are right, the question is now how to measure this properly. My idea would be - how much weight can an average person lift with the back and neck?

Then the formula f = m×a could be applied. Is that correct so far?

4. Feb 23, 2015

### A.T.

The external forces the body creates are very different from the muscle forces, because of leverage. And F=ma is not useful here at all.

You should rather look for literature on muscle parameters like maximal force, or physiological cross sectional area and maximal muscle stress (multiply the later two to get maximal force).

5. Feb 23, 2015

### freexd

Wow that's a lot more complicated then. One has to determine the force of each single muscle involved in the movement.

Regarding that, I would be glad if you could give me at least some estimatations. When we take for instance 1000N as number, would that be probable? I have not the imagination how strong 1000N is, like you probably have.

6. Feb 23, 2015

### A.T.

Of what? You still haven't said which forces you are interested in.

7. Feb 23, 2015

### freexd

Because I don't know how to describe it. The muscels cause the whole body to move. The body weighs a certain weight. To move the body the muscels have to create a certain amount force.

8. Feb 23, 2015

### jbriggs444

The whole body does not move in a single direction with a single acceleration. Instead you have a multitude of little forces acting in various directions. There is no one right way to summarize all of that information into a single number that says "there was this much total force".

9. Feb 24, 2015

### freexd

Ah ok, guess that means my question can't be answered and an estimation is also not possible?

10. Feb 24, 2015

### A.T.

Hard to say, without knowing the actual question.

11. Feb 24, 2015

### freexd

Seems like jbriggs understood my question.

12. Feb 24, 2015

### jbriggs444

I understand that you are after a single number that reflects the strength of the jerk. What is less clear is exactly how that number would be defined, how it would be measured or how it would be useful.

It sounds very much like the kind of number that a show like "Sports Science" would use. Such shows specialize in coming up with single, precise and surprisingly large numbers that incompletely characterize complex actions.