So I found this Quora question answerthat says that one cannot get a concussion from shaking their head too hard or rapidly because that can’t produce 80 Gs and 80 Gs is what is required for a concussion - but yet other sources said that it is perfectly possible to get a concussion from head-shaking too rapidly…which is right?
You may be interested in this research published in the British Medical Journal:
Head and neck injury risks in heavy metal: head bangers stuck between rock and a hard bass
It is characteristically thorough:
Wouldn’t 80G require accelerating the head at about 800m/s? I don’t think boxers punch that fast.
Acceleration is not velocity. 80g is 800 m/s per second. That doesn’t mean that you need a velocity of 800 m/s: You could also do it with a velocity change from, say, 20 m/s to -20 m/s over the course of 1/20 of a second.
As, for example, my own concussion as a teen where I flipped my bike and smacked headfirst into asphalt. I can well believe that sudden stop exceeded those limits.
There is two misapprehensions in the o.p.p. First, acceleration is not force; a static acceleration will produce a force in proportion to the mass but to describe a force as “80 g” is meaningless. Second, and more important, in terms of damage due to a sudden impulse such as a head hitting pavement is actually due to the derivative with respect to time of acceleration, called the “jerk” by physicists. This sudden change in acceleration causes the snapping feeling when you get into a car accident or the disorientation on a rollercoaster as the vestibular system isn’t able to keep up. However, there is no instrument to measure jerk directly, so it is typically described in an acceleration time history and colloquially referenced by the peak of the measured acceleration, e.g. “80 g”; it should really be stated in a way that describes the diration and character of the acceleration history, such as “an 80 g half-sine pulse over 10 milliseconds” from which a jerk or shock response spectrum (SRS) can be calculated.
As for the question of the o.p., I don’t think it would be possible to give yourself a concussion just by shaking your head, not because the human muscular system cannot produce sufficient impulse, but because a concussion requires a high differential between the motion of the skull and the brain within it, and there is too much inertial in the head for the muscles of the neck to create sufficient jerk. This requires some kind of an external force to stop the head violently. It is not a transfer of impulse through the skull and directly into the brain matter but rather the brain moving and impacting the inside of the skull, hence why hard football helments do not adequately protect against chronic traumatic encephalopathy (CTE) and may even exacerbate encouraging players to strike with the head.
Stranger
That is one mechanism of brain injury (often referred to as “coup-contrecoup” injury) but brain damage associated with concussion is not by way of brain hitting skull, contact injuries, or evenlinear, translational forces, but a result of rotational force leading to diffuse axonal shear damage. How much rotational acceleration/deceleration it takes is dependent on many variables.
Best guess based on the data that exists?
Can someone shake their head rotating it at more than 6.0 x 10^3 rad/s2? I dunno.
Also, the brain isn’t uniform or uniformly protected. Dr. Muriel Lezak, who wrote one of the excellent neuropsychology textbooks, used to tell her lecture audience that if you must take a blow to the head, try to hit from the front since the sides of the brain are much more inadequately protected from impact. This may or may not matter in the head banger scenario.
FWIW.
Measured angular acceleration males maximum doing activities of shaking head less than with jumping up and down as high as possible and that max was near an order of magnitude less than the one quoted above (931.25 rad/s² with head shaking max at 216.19 rad/s²). So it seems improbable that someone without an existing predisposition (be that past injury or other) could be able to generate enough angular acceleration by shaking their head.
Now the headbanging article cited concludes that a theoretical headbanger keeping a beat of 146 bets per minute with a range of 75 degrees could cause mild injury. Of note Wayne and Garth hit 138 bpm at 45 degrees but the only example they document of hitting or exceeding that rate and range is in a cartoon … Seriously I am not sure how possible it is for a real person to hit that rate at that range…
Party on, Wayne.
I was always taught rotational forces were more significant. But when I studied mechanics we basically used a complicated equation for acceleration that incorporated various linear, angular and Coriolis accelerations. Angular jerk might be more relevant. And people probably differ significantly - elderly people and babies have much different risk levels. It’s not that easy to study concussion — the current understanding is that it is much more common and pernicious than previously supposed.
This. When (for example) you review video of NFL concussion incidents, they almost always involve sudden starting/stopping of rotation of the head. This is supposedly why side-impact car crashes have been historically difficult to deal with: your body (including neck) gets accelerated sideways, and your head gets dragged along sideways by your neck, making it rotate, and your head comes to a sudden stop when it hits the window frame or edge of the roof. Your brain continues rotating after your head comes to a stop; the only thing that can bring your brain rotation to a stop is its connection with the brain stem.
There was a study done in the '80s in which baboons had their heads subjected to violent rotational accelerations in an attempt to understand what sorts of accelerations were required to reliably cause brain injury; the rotations weren’t far enough to cause neck injuries, but they were rapid enough so that the brain didn’t keep up with the skull, causing the sort of shearing damage that DSeid mentioned. They used a machine to cause the rotations, which allowed them to deliver measurable, repeatable motions. There were ethical problems in the conduct of the study; you read about them at the Wikipedia link, or search YouTube for “Unnecessary Fuss” to see the actual injurious rotations being inflicted. I don’t know whether they actually published any results, but the nature of the research - studying rotational accelerations rather than linear accelerations - tells you where the real problem is for brain injury.
When I was working for a defense contractor I spent some time in the environmental test area* and we had a new secretary poke her head in once, intensely interested in seeing a 100G test that was about to be run. “Okay, but you’re going to be disappointed,” I said. She was; the plate with the box on it hummed at about 50Hz and you couldn’t even see how far it was traveling up and down. I made sure she was there for the booster separation test where a 500-lb weight is raised about 15-degrees off vertical then released to whack against the framework with a most satisfying clang.
*Not doing anything cool, mostly gluing on the accelerometers and screwing the item down to the test bed; I didn’t even get to push the button.