Size Matters

We’re told that “size doesn’t matter,” but we all know it does. In reality, inadequate size severely limits your likelihood of playing NBA hoops or becoming president. Conversely, ex-Sumo wrestlers never become Kentucky Derby jockeys or fighter pilots. Basic anthropometrics like height, reach, and hand dominance follow us everywhere and influence how we perform physical tasks. But what does it mean in MMA? What can weight classes tell us about knockout rates? Let’s settle it once and for all.




Heavyweights score more knockouts, almost three times the rate of lightweights. A graph using only weight classes to predict KO/TKO finishes showed a direct correlation between weight and knockouts, validating this key relationship. Spanning the 110-pound journey from lightweight to heavyweight almost triples the rate at which TKOs occur. That’s a big difference. You can correctly bet heavyweight fights will end by strikes more than half the time, while betting against lightweights finishing by strikes will get you paid 80% of the time. Analysis of data from Strikeforce revealed a similar pattern. It’s true, size matters.


The idea of knockout power drives this relationship. Some guys have it, some don’t– but size is a key ingredient. Shane Carwin remarked that once his hands  touch people, “they go to sleep.” However, he is using more than just his hands. Muscles are like engines—they burn fuel, converting chemical potential energy into mechanical kinetic energy. Muscles enable physical work. The simple result is that heavyweight fights often end by strikes because more muscles do more damage.


Assisting heavyweight knockout artists is higher power striking accuracy. In the critical metric for knockout blows—power head strikes—heavyweights beat all other weight classes in accuracy. This is likely because heavier fighters are less agile, and their reactions are slower. More mass takes more effort to move due to inertia. Higher heavyweight accuracy is even more pronounced in the clinch and on the ground. Conversely, quick and elusive lightweights have the lowest accuracy of any weight class across the board. Are lightweights poor strikers? Probably not, their opponents are just faster.




When fist meets head, energy is transferred between them, and collisions like this are governed by physics. Isaac Newton determined that force equals mass times acceleration (F=ma). Physics is merciless. There’s no secret to this “Force,” and there’s no magical bracelet you can wear to break its laws or hide from its unrelenting truths. Monstrous 3XL-gloved fists with correspondingly massive arms, back, hips, and legs, are capable of inducing rapid acceleration of a human head upon contact. Collisions are also governed by momentum, which equals mass times velocity (p=mv). In a direct strike, conserved momentum accelerates the head quickly, causing the brain to bounce within the skull. This causes concussion injuries or knockouts. Both governing equations rely on mass, so bigger is better.


But momentum also relies on speed, and if lighter fighters have quicker hands, they should have more KO’s, right? No. The much larger mass of heavyweights dominates any increase in quickness of lighter hands. Larger fighters are also taller, with longer arms and reach. While it takes more energy to get a big arm moving at high velocity (inertia again), longer arms also have a longer runway to accelerate before they run out of room and finally stop at maximum reach distance. Shorter arms of lightweights may snap into action quickly, but can’t accelerate for long.




Realizing the chances of scoring knockouts at lightweight are drastically reduced, smaller fighters have attempted to win on the ground more often. The physics of the situation has changed the way fights unfold. Lightweights attempt 72% more takedowns per fight than heavyweights and 95% more submissions. A lightweight’s increased chances of surviving a few direct strikes means more time working submissions than heavyweights. Ultimately, we’ll see better BJJ among the elusive, lighterweights, where their skills can shine, rather than at heavyweight, where they’re only one crashing meat paw from Octagon nap time.


• More than half of heavyweight fights end via strikes, but few by submission.
• Almost half of lightweight fights go the distance, but few end via strikes.
• More muscle means more acceleration of your opponent’s head, which is bad (for them).
• Fighters adjust their fighting style to account for size.
• Size matters.

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