Physics of BJJ: How to Choke Me Out

Physics of BJJ: How to Choke Me Out

Brazilian Jiu-Jitsu (BJJ), the ground based martial art, is well known for its utilization of leverage for which a smaller, weaker person can effectively defend against a larger, stronger opponent. One way to neutralize an opponent is by way of a joint lock, which uses leverage to maximize the amount of force applied against certain joints to either hyperextend or dislocated them. Another way to neutralize an opponent is by way of a blood choke, which impedes blood flow from the heart to the brain. This concept is utilized in techniques such as hadaka-jime (rear naked choke) or Okuri-Eri-Jime (the bow and arrow choke), as well as many others.  

 

Figure 1: Two examples of blood chokes being shown, hadaka-jime on the left and sankaku-jime on the right. 

Blood chokes, whether it be with one’s arms or legs, work by constricting the carotid arteries, which is the major blood vessels below the chin that act as a major supplier of oxygenated blood to the brain. The carotid arteries are apart of an arterial system that is responsible for the transport of oxygenated blood to the tissues, as well as maintaining a relatively high arterial pressure. This arterial pressure is dependent on the elastic nature of the arterial wall; therefore, the cross-sectional area (A) of the arterial wall is dependent on the pressure difference over the wall, known as transmural pressure. Blood pressure can be written as the liquid pressure formula, ptr = ⍴qh + p0, and can be graphically represented by the graph showing the relationship between relative transmural pressure and relative cross-sectional area. 

When the choke is applied correctly, a significant amount of force narrows the cross-sectional area of the arterial wall, limiting its ability to expand. This, in turn, decreases blood pressure and the amount of oxygenated blood going to the brain. Vice versa, the choke causes the compression of the jugular vein, preventing blood from the head to be recirculated by the heart. After 20 seconds of a correctly applied choke, the average person loses consciousness, but regains consciousness without any lasting injury once the choke is released and blood pressure stabilizes.