So, I decided to write this take because there is confusion from a lot of people. Whenever a smaller person beats a much larger and stronger person, a lot of people get surprised because they didn't expect that. Some people still think that height, weight and strength are decisive in hand to hand combat, that has already been debunked. Size only becomes decisive if you fight somone that is literally as big as the Empire State Building and nobody is that big.
Height, weight and strength only give a person advantages but it doesn't mean that the person with the size and strength adavantage will always win. Masakatsu Funaki who stands 6'0" and weighs 209 lbs managed to win a MMA fight against Semmy Schilt who is 6'11" and weighs 290 lbs. Most of the reasons why smaller people are able to subdue larger and stronger people, have to do with physics. I'm not saying that the smaller person will always win, I'm saying that the larger person won't always win.
1. Reach advantage when striking only works when standing
A taller person has a reach advantage when they are standing. In that case the smaller person needs to take the larger person down. Once the taller person is on the ground, they no longer have that advantage.
2. Smaller people take away most of the larger person's strength advantage by taking them off their feet
A larger person's strength advantage includes the ability to pick up a smaller person, throw heavier punches and some standing holds that rely on strength. Most of the strength techniques require the use of a person's hips and weight. Once the smaller person brings down the larger person, most of the strength advantage is neutralized.
3. Smaller people have less center of gravity
The shorter a person is, the harder it is to initiate a takedown. This will also make certain techniques like throws easier for the smaller person.
4. Small Joint manipulations
While small joint manipulations are illegal in most MMA promotions, these techniques are self defense techniques, since they are very effective against larger opponents because they target a person's small joints. No matter how strong a person is, their fingers will always be delicate. Even if they have a super grip, they aren't impervious to small joint manipulations.
5. Too much muscle mass can be a disadvantage
While having a lot of muscle mass does mean that you'll hit harder, you'll also be slower, less flexible and you'll get tired faster. This is the reason why some of the best MMA fighters have lean muscle instead of large muscle mass, they don't look like body builders. Mariuz Pudzianowski(pictured below) who is one of the strongest men in the world, became a MMA fighter. He started at 310lbs but he had to drop down to 260 lbs because he got tired fast in his fights. Notice his transformation.
6. The larger opponent has trouble getting a secure submission or joint lock on a smaller person
Smaller people can escape from submissions and joint locks easier. The reason why is because of their smaller bodies. Think about it like this. You can pick up a 3 pound stone with ease, however if you want to pick up a very small pebble, you need to use your dexterity in order to pick it up. Same thing, in a fight.
7. Smaller people can apply joint locks and submissions much easier on larger and stronger opponents
As a result of their opponent's larger bodies, the smaller person will be able to get a secure grip when they lock on submissions and joint locks on their larger opponent. In martial arts, dexterity is a important factor because you need precision and agility with your hands to be able to apply a submission or joint lock on an opponent. Fedor Emilianenko who is 5'11" and weighs 235 lbs managed to defeat the 7'2" 350lb Hong man Choi by using a arm bar submission.
8. Smaller people have better maneuverability when fighting larger people
A smaller person can change positions and out maneuver a larger person as a result of having less reach. It's much harder for a larger person to try to outmaneuver a smaller person since they have longer reach.
9. Reflexes and quick thinking
In order to be a successful martial artist, you need to be able to dodge, block and quickly escape submissions. This all has to do with your reflexes and quick thinking. Anybody can have good reflexes but smaller people tend to demonstrate these more when they fight larger people because they can't afford to take too many hits from big bruisers. They use reflexes to counter attacks and eventually bring down the larger opponent.
9. Two people of the same weight but different heights will have strength differences
There are rare occasions were a smaller person weighs just as much as the taller person, the smaller person will always be stronger than the taller person of their equal weight.
10. Leverage and momentum
These are two things that various grappling arts focus on. A smaller person can use the larger and stronger person's momentum to take them off balance and they can use leverage to apply certain submissions on a larger and stronger person.
11. Limb targeting
In MMA there a fights were a smaller fighter targets a limb of the larger and stronger opponent. They do this to weaken that limb. Usually they'll target the knees in order to take down the larger opponent. You can see this strategy in the video and the result of this happens at the 8:20 mark of the video.
These are explanations as to how smaller people are able to win fights against larger and stronger people.
Most Helpful Opinions