Is it possible for an untrained person to incapacitate someone else with a strike to the solar plexus? If not, what kind of training does it require? If so, what is the most effective way to strike (with a punch or a knee) ? And how should you locate the solar plexus (maybe it is different in different people) ?
An untrained person will probably not be able to hit a live, moving opponent there meaningfully since they lack the technique, power, and accuracy to make this work. It would be better to simply aim to hit in the general abdomen area since while not as effective, it should make an effect and with a bit of luck, it can hit the solar plexus as well. Also, the elbow, front knuckles of the fist, toes/ball of the foot, and anything that looks or works like a stick are the means to properly trigger the solar plexus. A knee will hurt but mostly does other things via collateral damage as it is just too big to hit there directly.
What is the solar plexus and where is it?
As I described in this answer of mine, the solar plexus is a point where a lot of nerves and other tissue come together. It is positioned behind and just below the sternum regardless of the person as this is vital anatomy. The structure is actually pretty close to your spine with only your aorta in between, which means you need some penetrative power to reach it. Also, the rib cage does a good job of protecting vital areas, so the hit has to be as close as possible to the sternum without being hindered by the surrounding bones.
What is the effect of hitting it?
A direct hit will let the nerves fire. Since a lot of nerves come together, a plethora of things can happen, including
- nausea, since the stomach is directly in front of the solar plexus, so you obviously have to hit this organ hard in order to reach the latter at all
- a spasm of your diaphragm, meaning you are unable to breathe in until you stretch it by fully breathing out
- a rapid fall of your blood pressure via the vagus nerve, which can lead to dizziness, disorientedness, and sometimes loss of consciousness
- in very rare cases death, as your heart can come out of rhythm due to the neural shock and, if you are able to compress the aorta, the interruption of the blood flow into the anterior chambers. So it can literally stop your heart but this is indeed very rare
What does it need to incapacitate someone with a hit there?
Obviously, you need enough force to compress the tissue and organs that lie in front of the solar plexus. Also, you need to hit the right spot, just under the sternum and between the bows of the rib cage. This means you need
- power via a good technique
- penetration via a small area of impact (toes/ball of the foot, front knuckles, pointed elbow, or ideally the end of a bat/stick)
- good aim
Ideally, you have also set that up by a hit into the abdomen area directly before the impact so that the abdominal muscles are in a process of relaxation and put up less resistance.
Can an untrained person do that?
Theoretically, yes, of course. But as you will know by now, this would be quite a feat and definitely not something that you can rely on. Hitting someone hard there is not easy.
What can you do to train this?
You have to train a lot of technique for aim, proper area of impact, and power as well as spar a lot to get a feeling for movement and distance. This will include a lot of work on the heavy bag where one can mark a target area with tape for teep kicks, punches, and elbows in the appropriate height. As often in martial arts, there is no shortcut. If you have some sort of stick (e.g. solid umbrella) for self-defense purposes, you can repeatedly try to hit a random spot on a piece of wood while moving around.
It is possible but very unlikely that an untrained person will incapacitate someone with a strike to the solar plexus.
The solar plexus is easy to find. It's about 2" to 3" below the sternum.
The problem for the untrained is that it has to be hit fairly hard and ideally at an upward angle to be effective. It's too high up for a knee strike unless you are very flexible or much taller than your enemy. A punch will do but that requires you to know how to punch. Likewise a kick will do but you need to know how to kick.
Another issue is that if your opponent has worked out enough the solar plexus gets toughened by the structure of the muscles. This is not a problem for most people you will come across but still worth mentioning.
If you hit someone there correctly it has two effects.
- They will struggle to breath
- They will fall to their knees
It doesn't last long though. I once got hit there in sparring by a 3rd dan Shotokan Karate instructor. He hit it absolutely perfectly with a simple front kick. I was on my feet again in about 2 minutes and breathing normally after about 15 minutes. That's a pretty exceptionally long time for a strike of this kind as far as I know. I would recommend following through with other strikes to actually give yourself time to get away.