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To be knocked out means to lose consciousness or pass out, usually due to a blow or series of blows to the head. A knockout (KO) in boxing occurs when a fighter goes down because of a blow or blows (to the head or body) by the opponent and the fighter does not get up within the allotted time. In judo or mixed martial arts, a knockout may also occur when the blood flow to the brain is cut off by using a chokehold that presses on the carotid arteries.

Most fighting arts also have a technical knockout (TKO) that occurs when a fighter is unable or unwilling to continue or when the referee stops the fight to protect a fighter from further injury. This article will deal with a knockout due to a loss of consciousness from a blow to the head.

What is a knockout

A knockout from a blow occurs because of the force of the blow, the duration of the blow (force over time), and where the blow lands. A knockout may be the result of an acceleration or deceleration blow to the brain.

An acceleration blow occurs when a stationary head is struck by an accelerating punch. A rotary blow is probably the most serious type of acceleration blow. It occurs when the head is struck, usually with a hook punch, which causes it to quickly rotate to the side, compress the carotid arteries on either side of the neck, and cut off blood to the brain. Another type of acceleration blow is an uppercut to the chin, which causes the head to snap backward cutting off circulation to the back of the brain.

A deceleration blow occurs when a fast-moving object (the head) strikes a stationary object (the floor). A deceleration blow may also occur when one fighter’s head hits the other fighter’s head with great force.

In a blow to the front of the head, the skull is accelerated backward so quickly that the brain cannot keep up. After the skull stops moving, the brain catches up, crashes into the bony skull, and its back portions are injured. In a blow to the back of the head, the same movement takes place, but the resulting injury is to the front portion of the brain, especially at the tips of the frontal and temporal lobes.

If a fighter does not go down, or even worse gets up without having his “legs under him,” it increases the fighter’s susceptibility to subsequent punches that may result in a knockout or even permanent injury.

Effects of knockout

The brain is composed mostly of soft fat like gelatin, so, for protection, it is encased in the skull. Most brain injuries due to fighting are closed head injuries when a blow to the head shakes or fractures the skull without opening it but still injures the brain. The severity of a closed head injury is measured by the duration of the loss of consciousness.

A blow to the head that stuns a person that can, but usually does not, result in a loss of consciousness is a closed head injury called a concussion. A concussion may cause temporary headaches or blurred vision, but it is generally not serious. I once received a concussion from a punch to the forehead that also caused a partially detached retina.

A loss of consciousness results from a pressure wave from the force of the blow. If the pressure of the wave is higher than the person’s blood pressure, blood flow to the brainstem is interrupted and the person passes out. As the pressure wave recedes and blood flow to the brain stem returns, the person comes to. A loss of consciousness for a few seconds or minutes is a mild injury and rarely results in permanent brain damage. Most fighters with such injuries are not admitted to the hospital.

A loss of consciousness of 1–24 hours is considered a moderate head injury. Most people with such injuries are admitted to the hospital. Moderate head injuries may or may not result in permanent brain damage. In a moderate injury, as the pressure wave recedes, the person does not regain consciousness because of secondary complications, such as:
  • Epidural hematoma. Bleeding from a tear in an artery in the space between the skull and the outer covering of the brain (the dura).
  • Subdural hematoma. Bleeding from a tear in a vein between the dura and the brain.
  • Intracerebral hematoma. Bleeding into the brain itself.
If not recognized and repaired, such complications may result in permanent brain injury or death. A loss of consciousness of 24 or more hours is a severe head injury that usually results in permanent damage.

In severe head injuries, the pressure wave recedes but, in addition to any epidural, subdural, or intracerebral hematomas, there may be brain lacerations from skull fragments, strokes from occlusions of blood vessels, and tears in fiber tracts. People who recover from severe head injuries may have paralysis of one or both sides of the body, and difficulty in thinking, speaking, and seeing.

Even if the person makes a full recovery, years later, at post-mortem examinations, speck-like hemorrhages, called petechial hemorrhages, may be seen in the brain. Sometimes small tears are found in the fiber tracts of the brain, called white matter, that transmit messages from one region of nerve cells, called gray matter, to another region. Although each mild injury is not serious, repeated mild injuries may have a cumulative effect and may result in permanent brain damage. As the tiny petechial hemorrhages and the tiny tears in the white matter accumulate over time, a person may begin to stagger, lose balance, experience short-term memory loss, and make movements as if they were still in the ring, called being punch drunk” I once worked with a guy who was a boxer in his earlier years. When he was standing around wasting time, such as in a checkout line, he would appear to be bob and weaving to avoid imaginary punches.

Causes of a knockout

A knockout, or loss of consciousness, occurs for one of three reasons:
  • The brain is injured as it bangs against the opposite side of the skull
  • There is a disruption in the nerve message systems of the brain. At the base of the brain is a small part of the brain stem called the reticular activating system (RAS). A disruption of the RAS may cause a person to pass out.
  • There is a disruption in blood flow to the brain. During a stroke, a loss of circulation to a part of the brain to a blood vessel blockage results in permanent loss of function. A knockout may also result in a loss of blood flow to the brain, but the result is temporary. If a person is punched “on the button,” or square on the jaw, the force of the blow is transmitted directly to the temporomandibular joint (TMJ) where it temporarily disrupts cerebral circulation. Disruption in blood flow to the brain can also be caused by the application of a stranglehold that causes a person to pass out. These holds have been used in judo with supervision for over a hundred years with no apparent permanent damage.


A knockdown is different from a knockout. In a knockdown, the pressure wave from the blow temporarily shuts down the inner ear, the balance control center, and stuns the fighter but it does not injure the brain.

Reviving from knockout

One way to revive a fallen or dazed fighter is to wave smelling salts under the nose. The salts are composed of ammonium carbonate and perfume to create a fast-acting stimulant that triggers the inhalation reflex. The fumes are absorbed by the mucus membrane in the nose and in the lungs, which triggers the muscles that control breathing to work faster, forcing more oxygen into the fighter’s system, and quickening the awakening. Although the salts may bring a fighter back to alertness, they may mask serious symptoms.

Susceptibility to knockout

  • Anatomy/heredity. Heredity, family history, body build, and genetics may affect a person’s susceptibility to knockout. Some fighters have a “glass jaw” and are easily knocked out, while others have an “iron jaw” and are difficult to knock out. These factors are fixed and cannot be changed by the fighter.
  • Neck muscles. If your head does not move with a punch, you will probably not be knocked out. Strong neck and upper shoulder muscles are what keep the head from moving, so they decease a fighter’s susceptibility to knockouts. Look at fighters who have a “neck like a bull,” Mike Tyson for example, they rarely are knocked out. To resist knockouts, strengthen your neck muscles.
  • Mouthpiece. Most people think a mouthpiece’s only purpose is to protect the mouth and the teeth. While it does do this, a well-made mouthpiece greatly increases jaw strength and dissipates much of the force of a blow before it reaches the brain and causes a knockout.
  • Chin tuck. If a fighter keeps the chin tucked, called having a “good chin,” the chances of a knockout are reduced. When the chin is up, it is more susceptible to being struck with a blow that rotates and hyperextends the neck, which makes a knockout more likely.
  • Under the influence. Being under the influence of illicit drugs, medications, alcohol, or steroids directly or indirectly predisposes the brain to a knockout. Even occasional use may be a problem if the substance is still in the system during a fight or if it has altered the brain’s function.
  • Head protection. Head protection helps prevent knockouts since it absorbs some of the force of a blow, and it helps prevent cuts and burst eardrums. Most head protectors have "ear channels" that dissipate the air pressure from a blow to the side of the head to protect the eardrum. While the head protector helps protect the head, it has not been proved to protect against brain damage:
  • Being constantly hit on the head is not a good thing for the brain. Even if people claim there is little risk of permanent damage to the brain from the being hit with blows to a head protector, no brain is ever helped by being hit with blows.
  • Head protection may even be a hazard since it gives fighters a false sense of security, and thus, they expose themselves to even more opportunities to get their heads struck by blows. Head protection that is too low in the front will cause the fighter to train with the jaw up, which trains the fighter to not keep the chin tucked. If a fighter constantly must readjust an ill-fitting head protector, it exposes the fighter to attacks.

Head trauma

A 2007 study led by Dr. Charles Hoge, a colonel and psychiatry chief at Walter Reed Army Institute of Research, was based on a survey of nearly 2,500 soldiers. The study found that one in six soldiers returning from Iraq had suffered concussions and that brain injury made traumatic stress more likely. The study tied only one symptom—headaches—specifically to brain injury.

Fifteen percent of soldiers reported a mild brain injury—having been knocked unconscious or left confused or "seeing stars" after a blast. They were more likely than other soldiers to report health problems, missing work, and symptoms such as trouble concentrating.

The worst symptoms were in soldiers who lost consciousness. About 44 percent of them met the criteria for post-traumatic stress, compared with 16 percent of soldiers with non-head injuries, and only 9 percent of those with no injuries

Helmet research

Kevin Guskiewicz, professor of exercise and sports science and director of the Sports Medicine Research Laboratory at the University of North Carolina, Chapel Hill, led research into brain injuries resulting from head impacts in sports. The research showed that even low-impact head hits can cause brain injuries. Players who look like they have been hit hard are not necessarily the ones who will sustain the most brain damage; there is no relationship between the magnitude of the impact and the clinical outcome.

The research used a helmet called the Revolution IQ HITS that uses six sensors to measure in real-time the amount of g-force a player's head experiences at impact, where the hit occurs, and where it comes from. G-force is a measure of acceleration against the Earth's gravitational pull. One g is a person's weight at sea level. In car crash tests at 25 m.p.h., dummies hit windshields at 100g. Football players commonly experience hits at forces between 50g and 100g. Previous research suggested that concussions likely resulted at forces above 75g, but the new study indicates otherwise.

Between 2004 and 2006, University of North Carolina football players wore the helmets during practice sessions and games. Some players sustained concussions undergoing hits just above 60g while others had no sign of injury after a hit above 90g. Other findings showed that a single knock to the head at an impact greater than 90g does not always result in immediate concussion symptoms, such as a headache, nausea, blurred vision, or ringing in the ears. Location, not necessarily force, seemed to play a significant role in brain injury. Six out of 13 players that sustained a concussion had experienced impacts at the top of their head, as opposed to the side.

Knockouts preparations

Pre-fight preparation

A fighter who has not properly prepared for a fight is more susceptible to a knockout. Preparedness includes:
  • Proper training.
  • A safe weight loss regimen.
  • Avoiding dehydration.
  • A good conditioning regimen.

Post knockout

If you get knocked down or knocked out in training or in the ring, you are susceptible to another knockout or permanent damage if you do not properly recover before fighting again. Honor your school’s knockout rules or any fighting suspensions and you will live to fight again.

Just before the loss of consciousness is a period of anterograde amnesia that results from an erasure of those memories laid down before the loss of consciousness. The duration of the anterograde amnesia is proportional to the duration of the loss of consciousness. Because of this amnesia, a fighter will probably not remember what occurred just before the knockout occurred.

Once consciousness is regained, there is a period of retrograde amnesia that results from an inability of the brain to lay down permanent memories after a loss of consciousness. The duration of the retrograde amnesia is proportional to the duration of the loss of consciousness. Because of this amnesia, a fighter will probably not remember what occurred for a few minutes after coming to after a knockout.

Avoid them!

Knockouts are something every fighter who is concerned about his or her health, now or in the future, should avoid. Knockouts and blows to the head are not good for fighters. Boxers with more than 50 professional bouts often have obvious Alzheimer like symptoms as well as MRI and psychological test abnormalities.

In his book, Brain Damage in Boxer: A Study of Prevalence of Traumatic Encephalopathy Among Ex-Professional Boxers (London, Pitman, 1969), A. H. Roberts reported that 15-40% of former professional boxers had some symptoms of brain injury. He found that the longer the career and the more professional fights a fighter had, the greater the prevalence of brain injury.


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