Physics in Martial Practice

A month ago I found a YouTube video where a submission coach was explaining how an eye gouge was not the best defense against the rear choke. I agree that a proper applied choke is very difficult to defend in many cases, however it was the way this person was applying the eye gouge that caught my attention. The rear naked choke (RNC) is used as a submission in MMA, BJJ and other combat sports. As a result it has been normalized as a way to control an aggressive person by trained and even untrained individuals (even kids) despite its dangers. Use of force expert Dennis Rovere had for years warned about the use of such techniques by security and police personnel. We will now cover couple points that can be used to enhanced the effectiveness of empty hand and armed techniques using physics to demonstrate our reasoning.

Flat vs. Curved Fingers

I trained Qin Na techniques with Dennis Rovere and Willy Lin where an emphasis to keeping the fingers curved was a must to increase effectiveness. In the Xingyi Nine Songs translated by Mr. Rovere there is a passage that reads:

“Song #5 Fingers. All five fingers are slightly separated and take the shape of hooks. The tiger mouth is rounded so that the position looks both strong and soft. Power should reach the hands” Rovere, D., Journal of Chinese Martial Studies, Summer 2011, Issue 5.

The above paragraph comes from old Chinese writings and shows that using curved fingers is nothing new when applying techniques with the fingers e.g., joint locks, eye gouges, pressure point attacks etc. Other Chinese martial arts like Eagle Claw (Ying Zhao Pai, 鷹爪派) also stresses this point. Going back to the video against the rear choke, the demonstrator was using flat fingers when applying the eye gouge, he would encourage his assistant to apply more pressure while closing his eyes to show that the eye gouge was pretty much useless. We will make use of some basic physics calculations to demonstrate the difference it makes when using flat vs. curved fingers. As a disclaimer it’s been years since I done any of such calculations and to be honest physics was never my favorite subject in school.

Curved fingers

First we need to define what the average grip strength is for men and women as reported in the literature. These values will vary based on size, age and the physical attributes of the person.

Men: 72.6lbsf

Women: 44lbsf

Incorrect way to apply an eye gouge

We now need to determine what the required average rupture pressure for a human eye is, from literature we have 0.91 ± 0.29 MPa or (132 psi ± 42psi). Calculating the areas used to apply pressure using a flat thumb vs. the tip of the thumb using my own measurements are:

Flat thumb: 0.75 sq in.

Curved thumb: 0.125 sq in

The expression to calculate the pressure applied is:

The pressures than could be applied by a woman using flat vs. curve fingers are:

Flat: 44lbsf / 0.75 sq in. = 58.6 psi (where lbsf/sq in = psi)

Curved: 44lbsf / 0.125 sq in = 352 psi

From the above we can conclude that using curve fingers when applying joint locks or eye gouges the pressure applied increases by 6 times! enough to damage the eye. Now imagine if on top of using curved fingers when applying the eye gouge we add long nails… We can conclude that even if the choke is held, serious eye injury can be exerted on an attacker by a simple modification when applying such technique.

Phoenix Eye

This concept can also be applied to striking. Due to the use of padded gloves and other protective equipment it is not possible to make use of this concept. However, in a self defense context where there is no protection, we can use attacks with smaller areas to delivered more damage to an attacker’s weak points e.g., striking with two knuckles rather than with the flat of the fist, phoenix eye punch etc. It goes without saying, hand and body conditioning is required to be more effective e.g., post or sand bag training. The opposite can also be used, by increasing the area of contact when blocking certain kicks helps distribute the striking pressure to reduce damage on the defender.

Hand conditioning

Striking with Weapons

Part of my Chinese Military Sanda training with Mr. Rovere included the use of the police baton. Some of the basic parameters to considered were the understanding of the capabilities of the particular weapon e.g., cutting, stabbing, striking, reach etc. The prefer way of wielding the baton was to make use of its full length, not only to keep a safe distance but also to enhance the amount of force to be delivered. Other martial arts tend to use the baton/stick to strike with about the middle of the weapon while the preferred Chinese method is to do so with the first couple inches from the tip. We will once again use physics to demonstrate the most efficient way to use a baton/stick for self protection.

For this calculation I used a fixed baton and an Arnis stick for comparison and the equation for inertia for a uniform rod to simplify the process. The inertia calculation about the center of mass (CM) is:

The calculation for inertia at the end of the rod is:

The results confirm that more force can be applied when striking with closer to the end tip, by about 4 times. Similarly, the weight of the stick adds to the force than can be applied. This concept can also be use when striking with the hands or feet. Another element that can be added is dropping the weight of the arm, shoulder and body to accompany a downward strike to enhanced the force delivered.

Newton’s 2nd Law states “A body in motion tends to remain in motion at a constant velocity unless acted on by a net external force”, we can then assume that the inertia generated is equal to the force required to stop it, here we don’t considered any other factors e.g., elastic deformation of the objects and others. As calculated above keeping the right distance is important, we understand that this is not always possible, as combat is dynamic. However, understanding the advantage of managing how close we are to the opponent using footwork to stay at a safe distance and to be able to generate maximum force is important. This short post covered basic elements that we hope can help enhanced your own techniques.

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