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Bone Crushing Power: Force Of A Fighter

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Almost one month ago photos of UFC fighter Stefan Struve’s broken jaw were swirling the net after losing to Mark Hunt by TKO on Fuel TV.  Many discussed the shock and awe around such a gruesome fracture, however few went into the details of just how something like this happens.  We’ve been going over a ton of data at SciFighting to try an answer to this and many other questions around strength, power and damage in MMA.

Stefan Struve vs. Mark Hunt

First you should know some interesting facts about human bone.  Bone is one of the most resilient materials on the planet.  Ounce for Ounce, bone is stronger than steel.  A bar of steel of comparable size would weigh four to five times as much as bone.  In principle, a cubic inch of bone can bear a load of up to 19,000 lbs. (8,626 kg) or more, roughly equivalent to the mass of five standard pickup trucks – which makes it about four times as strong as concrete.

However, the speed at which force is delivered affects whether bone can actually withstand such loads.

A study in 2010 by Cindy Bir (Biomedical Engineer) at Wayne State University in Detroit investigated boxers and found that they could generate up to 5,000 newtons of force with a single punch.  That is more than the force exerted by a half ton of weight on the Earth’s surface.  During the same study they also looked at kicks from several different fightingstyles and determined that experts could generate up to 9,000 newtons of force with them.  That is roughly equal to a ton of force.

Further research during the study also showed that a quick, sharp blow that delivers approximately 3,300 newtons of force has a 25 percent chance of cracking an average individual’s rib.  Although it takes more force, appx. 4,000 newtons,  to fracture the femur (the long bone in the thigh that supports most of the body’s weight when standing upright.

All that being said, the force alone won’t guarantee you will or won’t break a bone.  Much of this has to do with how much fat and muscle tissue is surrounding the area.  The more padding around the bone the more likely it is to absorb the force of impact, thus protecting the bone.

Struve vs. Hunt

Another interesting bit of data that Cindy Bir and her team found during their research surrounds knock out blows.  The amount of force in a punch or kick doesn’t necessarily guarantee a knockout.  In order to knock someone out you need make the head whip around in a rotational way.  The shear force from a strike that whips the head back stress out neurons and thus the brain shuts down as a protective measure.  A strike that makes the head spin at a rate from 0 to 43,000 rpm in just one second had a 25% chance of knocking a person unconscious.

This is one reason why fighters tend to strengthen their neck muscles.  The stronger your neck is the less likely a strong impact will cause it to whip around.  However, if you are caught off guard the strength of your muscles won’t help you much.

Knowing all this we can begin to make some solid assumptions about how and why Stefan’s jaw was broken by Hunt’s knock out blow.  Taking a look at Stefan’s stats we see he is currently 25 years old, 7 feet tall and weighs 260 pounds.  He is definitely in the heavyweight class.  His opponent in the fight (Mark Hunt) is currently 39 years old, 5 foot 10 inches and weighs 265 pounds.

Bone Remodeling

For most individuals bone ossification (growth and development) is complete by about age 25.  Even after age 25 bone is continually reabsorbed and and deposited by cells in the body called Osteoclasts and Osteoblasts (respectively).  Starting at age 40 Osteoblasts begin to slow down and bone deposits occur more slowly.  This results in bones becoming more brittle as we age.  For the purpose of this exercise it’s safe to conclude that both fighters had bone at peak strength for their physiques.

Since both fighters are within 5 pounds of each other you might assume the strength of each fighter is similar, however we don’t have any data on percentage of lean mass to fat mass for the fighters so there is certainly a margin of error we can’t account for.  Just for argument’s sake we will assume both are at or below 12% body fat.

Now let’s look at height.  Stefan is a towering 7 feet in height, whereas Mark is just 5 feet 10 inches.  It’s important to note that a fighters weight alone doesn’t imply they can recruit that weight and use it towards a strike.  Looking at Mark Hunt we see he is simply more dense in physique than Stefan Struve.  That means he has the ability to recruit more strength to deliver a devastating blow.  Even with bones of the same thickness between the two fighters, a shorter bone will be more resilient to punishment.  The longer the bone the easier it is to apply pressure to a weak point in the structure.

Common Jaw Fracture Points

When considering reach, Stefan’s is a massive 83 inches whereas with Mark it is a more modest 74 inches.  Some may argue that reach doesn’t tell us much as the way the measurements are performed you aren’t getting an accurate picture of an actual reach advantage.  However, for the purpose of this exercise we are only concerned with the distribution of mass.  Here we see more evidence that mass on Mark Hunt is more tightly packed than on Stefan Struve.  This in essence tells us that the pounds per square inch of an impact from Mark Hunt will likely be more devastating than someone like Stefan Struve. Also since he is more dense, layered with more tightly packed muscle or fat tissue then we can also assume he can absorb strikes more easily than Stefan.

In conclusion given the research data and the factors of probability based on the two fighters builds it’s quite easy to see how Stefan’s jaw could be fractured by a single decisive blow by Mark Hunt.

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Luca Rajabi
Luca has been passionate about martial arts and eastern philosophies since childhood. As an athlete, inventor and entrepreneur Luca founded SciFighting on the principal lessons learned from his life experience "fighting" to preserve his health and fitness. Although born with inherently poor and inconsistent health he pushed forward to learn as much as he could about the sciences of technology, medicine and mental health. Years of study, working with physicians and combined analysis finally began to bare fruit by his early twenties. Starting with Fencing, cross training and body building then moving to Boxing, Western Kickboxing, Muay Thai, Brazilian Jiujitsu, Eskrima and an eclectic assortment of self defense techniques. Luca's core philosophy is that to win a battle every fighter must balance their mental and physical health. Luca has said that "With well developed technique, conditioning and mental focus a sound strategy will most often win over brute strength alone." It is in this spirit that he passionately advocates for the "Science of Fighting".