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SYFY WIRE Science Behind the Fiction

What happens when you get punched in the face? The science behind 'Rocky'


By Cassidy Ward
Rocky (1976)

Rocky, perhaps the most beloved sports movie of all time, opens on a small club boxing match on Nov. 25, 1975, forty-seven years ago this week. By the time the final bell rings, both fighters have taken such a beating that ribs are dislocated and eyes are swollen shut. At one point, Rocky (Sylvester Stallone) needs his eyelid cut just so that he can see well enough for the fight to continue.

Both fighters have taken blow after blow, straight to the head, and it shows. Even those of us who don’t get punched for a living will probably get bonked in the head once or twice in our lives. You might say the wrong thing to the wrong person and end up with a stranger’s fist occupying the same space as your face, or you might just forget to duck through a low doorway. We’re all destined for a solid smack to the skull eventually, so we might as well find out what that means for us and for Rocky.


From your body’s perspective, a well-thrown punch is like an asteroid. It’s coming in fast and hot, it isn’t going to destroy the planet, but anyone living on it the next day is going to have a bad time. When the punch hits, the force of that blow travels through your body like a wave, carrying pain and destruction with it. The harder the punch, the further that blow travels and the more damage it does along the way.

Your opponent’s fist hits your face and your skin gets displaced. It stretches, carrying blood vessels with it and some of those blood vessels will stretch too far. The wave of damage tears a bunch of tiny holes in the capillaries and blood leaks out beneath the skin, providing the telltale discoloration of a bruise. Over time, your immune system cleans up the blood spill, breaking down the red blood cells into other compounds, and changing the color of the bruise from dark blue or red to yellow or green.

We’ve all had bruises before and for the most part they’re no big deal, but that’s only the beginning of the pain train when you’re in the middle of a title fight.


Once the wave of destruction has torn through your blood vessels and spilt blood beneath your skin, it hits a wall of bone. Your bones, including your skull, are surrounded by the periosteum, a thin protective barrier around the bone that provides it with blood, nerves, and material for growing and healing. It will be the first to fall beneath the force of the fist.

As the kinetic energy moves through your skull it can damage blood vessels in the bone just the same as can in the skin. While your bones are tougher and can take a harder hit, you can bruise your bones if you hit them hard enough. If things get really serious, the bones can break.

Of course, the variables around whether a particular person will sustain a fracture from a particular activity are too numerous to satisfactorily account for, but scientists have done a number of studies that reveal a sort of range at which a skull will fracture. An interesting aspect of this research, though not directly relevant to today’s avenue of inquiry, concerns how much force is required to crush a human skull into a handful of bone dust.

Those same scientists, from Tokyo University, experimentally tested the force needed for a skull to fracture at the temporal region, a likely place to get hit in a fight. The force needed to separate the parietotemporal suture, the boundary between two of the skull’s plates, averaged at about 258 kilograms of force per square inch, though they did observe fractures with as little as 135 kilograms of force.

Black and white print of a human skull

The average force of a human punch is about 200 kilograms per square inch, so if you get in a fight with a stranger on the street, there’s a decent chance you’ll walk away without a skull fracture. It all depends on how hard they hit and how strong your skull is. If you get in a professional level fight, however, it’s incredibly likely you’re walking away with a bruised or broken skull. Pro boxers have clocked in above 600 kilograms of force per square inch in a single punch.


Once the force of the punch gets through the last layer of the skull, there’s nothing in its way but three pounds worth of fat and neurons that just so happen to contain every happy memory, every proud achievement, and every bittersweet moment you’ve ever experienced. As it moves through the skull it carries the head with it in the direction of impact, but the brain hasn’t received the message yet. Consequently, the brain bashes against the inside of the skull and bounces off. If there’s enough force, it might hit the other side of the skull and bounce off again. This process can continue, with the brain bouncing back and forth around inside the skull like a billiard ball, until it finally comes to rest.

Sure, there are blood vessels in the brain that can be damaged, so there’s some risk of bruising. Generally speaking, bruising your brain is something you want to avoid but it isn’t the weirdest or most dangerous part of a head injury. As the wave of force travels through the head and the brain jostles back and forth, the neurons can tear and snap. Not only can a destroyed neuron no longer carry out its duties transmitting messages, it also puts nearby neurons in danger. As they degenerate, they release toxins into the environment and kill nearby neurons. That spot of damage that pops up in the wake of head trauma is commonly referred to as a concussion.


If the injury is severe enough, or if it’s repeated often, as is sometimes the case with certain athletes, it can cause downstream problems that include chronic headaches, difficulty learning, problems with thinking and memory, and in some cases dementia. Your risk of these severe symptoms increases if you experience continued brain injuries as is inevitably the case in some sports.

Eventually, blessedly, the force of the punch either rattles itself away or exits out the other side of the skull and the wave of damage ends. Provided nothing traumatic happens again for a while, you’re body has a remarkable ability to recover from these sorts of injuries. But if you get hit again quickly, like if you happen to be in the middle of a competitive fist fight, then you might be in trouble. If you’re going to fight someone, either win or lose, but do it quickly.

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