Knockout: Humans Can Sure Take A Punch
The human body can take a remarkable amount of punishment, given
bones made of one of the strongest materials found in nature. At
the same time, even an unarmed person can inflict an astonishing
amount of damage with the proper training.
So how much does it take to crack a bone? And how much mayhem
can a person deal out? In an era when "extreme fighting"
has become a popular phenomenon, scientists are testing the extremes
that athletes at the peak of their game can reach in order to
help the rest of us.
"Understanding brain injury mechanisms all the way down
to the cellular level will ultimately help everyone, not just
athletes," biomedical engineer Cindy Bir at Wayne State University
in Detroit explained. "If someone has a brain injury in a
fall or motor vehicle accident, what we learn from athletes can
help as well."
Bone is extraordinarily strong ounce for ounce, bone is
stronger than steel, since a bar of steel of comparable size would
weigh four or five times as much. A cubic inch of bone can in
principle bear a load of 19,000 lbs. (8,626 kg) or more
roughly the weight of five standard pickup trucks making
it about four times as strong as concrete.
Still, whether or not bone actually withstands such loads depends
heavily on how quickly force is delivered.
"When you perform CPR, you can give chest compressions and
not break any ribs, but if you apply the same amount of force
quickly instead of slowly, and you can end up having rib fractures,"
When it comes to unleashing force quickly, Bir and her colleagues
investigated boxers and found they could generate up to 5,000
newtons of force with a punch, more than that exerted down by
a half-ton on Earth's surface.
When it comes to kicks, "they can obviously generate more
force, since there's more body mass behind it," Bir said.
After looking at kicks from several different fighting styles,
they found that experts could generate up to 9,000 newtons with
them, equal to roughly a ton of force.
A quick, sharp blow that delivers some 3,300 newtons of force
has a 25 percent chance of cracking an average person's rib, she
said. It takes more force to fracture the femur, Bir noted
maybe some 4,000 newtons since that long thighbone is meant
to support the body.
"That doesn't means that below those values you won't have
a fracture or above them you will," Bir said. The amount
of damage a blow inflicts also varies due to factors such as the
amount of muscle or fat covering a bone and the angle at which
the blow lands, as well as the age and health of a person, which
can affect bone strength.
Although it makes sense that a massive fighter can unleash more
powerful blows than a lightweight, "it's also about how much
of the mass of your body you can recruit," Bir said. "You
see some little guys hit with a lot of force because they know
how to recruit their mass."
Roll with the punch
When it comes to knocking someone out with a punch, "it's
less about the force of the blow than it is getting the head to
whip around, to move in a rotational kind of way," Bir said.
The shear forces from a strike that whips the head back stress
out neurons, and the brain shuts down as a protective response.
A blow that gives the head enough spin to go from 0 to 43,000
rpm in just one second has a 25 percent chance of knocking a person
"That's why you see boxers build up neck muscles
the thinking is that you can prevent that kind of motion then,"
Bir explained. "It's also about anticipating the blow
the ones that catch you off guard can be more of an issue."
Knocking the wind out of someone is also less about force "than
the impact occurring just right for it to happen," Bir said.
When it happens, the air isn't literally squeezed from the lungs,
but instead it is a matter of getting the diaphragm the
sheet of muscle under the lungs to spasm.
"A blow can cause your diaphragm to temporarily lock up
it's kind of like a cramp, and so it's hard for you to
take a breath," she explained.
The Biophysics of taking a punch
The sternocleidomastoids (SCM) -- one on each side of the neck
-- are paired muscles, composed of the sternomastoid component
that runs from the sternum to the mastoid process of the skull,
immediately behind and below the ear, and the cleidomastoid muscle
that runs from the clavicle to the mastoid. When flexed, the SCM
rotates the head toward the opposing side. Flexing both SCMs in
alternation shakes the head no, as one might if waving
off an overly concerned ringside physician. Flexing them simultaneously
flexes the neck forward and extends the head -- in the right circumstance
resisting the force of a blow to the face. Its why fighters
often seem to be ducking into a punch.
Moreover, arrayed against them are the muscles used in throwing
a punch: calves, gluts, lats, pecs, triceps, etc. These are some
of the most powerful muscles in the body. It is not surprising
then that we rarely see the thrower of a well-placed punch to
the head grasping his hand in pain and stumbling back in amazement
as his opponent casually flexes his SCMs and smiles; the muscular
arithmetic is firmly in the throwers favor.
When a punch of sufficient force strikes the face, it accelerates
the front of the cranium back into the frontal lobes of the brain.
This is the irreducible sweet science of brain injury. A gentle
blow to the frontal lobes causes various degrees of central nervous
system sedation -- it stuns the brain -- and a blow of sufficient
force simply shuts the brain off. Seizures are not uncommon.
When a blow to the head comes from an angle, as opposed to straight
on, only one of the SCMs can resist the force: The resulting acceleration
of the cranium and damage to the brain are thus much greater.
Worse still, when a fighter is struck on the chin, the mandible
creates leverage that magnifies the force and damage. This is
the phenomenon of a fighter being hit on the button.
Incidentally, this is an argument why, all things being equal,
fighters with large heads and Cro-Magnon-like chins are at a theoretical
mechanical disadvantage in withstanding blows.
The anatomy of the brain makes blows to the back of the head
particularly dangerous. The extensor muscles of the neck are far
stronger than the SCMs, but the part of the brain under direct
assault is more delicate. The frontal lobes injured in a frontal
blow control speech, movement and thought -- all the neurologic
skills we see depleted in old boxers. The back of the brain, the
hindbrain or rhombencephalon, controls respiration, heart rate,
swallowing, blood pressure. Fighters who sustain injuries there
never grow to be old.
A study would have to evaluate several variables
Due to the nature of our anatomy along with the biophysics of
how a person gets "knocked out", there would likely
be too many variables to ever scientifically determine just one
cause or "infallible protection" against a knockout.
Firstly, many knockouts are caused by an instant somatosensory
loss via the mandibular nerve, so you would first have to objectively
study how the a muscle absorbs impact while maintaining the stability
of the sensory root of this nerve.
Secondly, if we take the SCM as an example, you would need to
integrate and measure kinesthetics, isokinetics, and several dynamic
functions of the muscle during head impact. Since most knockouts
come from an angle (usually lateral), you would also have to establish
how the SCM, a muscle whose primary function is flexion and rotation,
would have the isometric or eccentric strength to help resist
the lateral impact of a blow in comparison to other muscles which
are stronger lateral resisters such as the upper fibers of the
traps and other cervical musculature, especially considering that
some cervical muscles exhibit very strong lateral flexion when
Also, an impact that produces a knockout has very little to do
with the strength or power of the blow, so the study would also
have to incorporate the dynamics and biomechanics of how a fighter
is hit and how and the impact precisely affects the anatomical
structures independent of the degree of force.
Wading into a fight
It can be hard to study how much damage a person can really give
"We try as best as we can to study athletes in their native
environment, so to speak, so more time in the ring, or during
bouts or fights the better that's when they're really fighting
to peak potential," Bir said. "It can be difficult integrating
equipment into that environment to measure them, since you don't
want to interfere with their normal functioning, such as sensors
that might decrease the protective effect of their gloves. The
nice thing is that technology is advancing and getting smaller
and wireless, to not get in the way of what people are doing."
The data that Bir and her colleagues might glean could help save
"We joke that if someone is willing to get hit in the head,
we should be measuring it," she explained. "If we know
what causes an injury, you can do simple things like develop better
protective gear and design bike helmets to help, say, 7-year-olds."
February 16, 2010