PONDERING THE PUNCH Finally Grasping an Intuitive and Scientifically Correct Understanding of the Physics of Striking

Neil A. Bednar

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Introduction Practicing martial arts for many years while making a living as a mechanical engineer I’ve become more and more interested in the technical dynamics of a punch, in the optimization of biomechanical energy transfer, and in physical methods used to execute these things. I’ve been taught how to punch by many different people and often these methods share a common principle; however sometimes they do not (or seem not to). This has caused frustration and confusion, especially when most martial arts teachers aren’t good with math and physics, and most physicists and mathematicians aren’t interested in punching. Although there must certainly be others out there with skill in both areas, I’ve yet to come across many well written explanations which use common language and utilize a consistent and technically correct physics-based approach which focuses attention to both the physics and the human being simultaneously. Problem solving in mechanical engineering often involves stepping back form the problem and reassessing. There is usually more than one way to solve a problem, but there are some ways which are better than others when it comes to understanding the problem intuitively, logically, or consistently. For example, people often talk about the “force” of a punch being an effective measurement of the quality of punch, yet few people step back and consider the technical details of such a statement. “Instantaneous force” is sometimes quoted in literature on the physics of boxing for example, but we typically aren’t told over what duration of time the force is applied, nor what the total force envelope looks like. The point is that the “maximum force” of a punch is much like the “maximum speed” of your car on your drive to the corner store. There is a maximum, but you don’t drive the maximum speed for the entire duration of your trip. The details of what happens during your drive, or in our case what happens during the time the fist is in contact with the target are the key to unlocking the secrets of punch dynamics. If you stood against an opaque curtain and someone punched you in the stomach, there’d be no way to see what was going on behind the curtain. From the perspective of the person being punched it doesn’t really matter, because the important thing is how much damage is being done, how much energy is being transferred into your gut. I’ll explain the technical details, the correct physics of these things in this paper. Look at a hydraulic ram- it can easily produce 10,000 lbs. of “force”, but these usually move so slowly that getting hit with it when it’s barely moving and when you can just step back as you watch it move isn’t something that’s going to injure you. In addition, even a fast moving hydraulic ram with the same 10,000 lb. force capability might have a large surface area which would likely just push you back rather than break your bones. Further to the point, consider a hydraulic ram with a smaller, fist-size surface area- what would be the difference if it hit you with 10,000 lbs. of force or 5,000 lbs. of force? What if there was a spring on the end of the ram?

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Given these considerations, is the “force” of a punch the most important thing to focus on when analyzing a punch? If it is, then what would you do about that? What is a “force” really anyway? What about “momentum”? How about “speed”? It all seems pretty confusing. It’s important to realize that we as human beings, although capable of amazing feats of physical prowess and endurance, are not machines. We all have limitations and these vary, so although there may be a theoretical “best practice” to optimize a particular punch, there will always be the human element to deal with. Sometimes it is a hard-stop, and sometimes it is just one more challenge to overcome. What’s needed is a good explanation- a way of looking at an event like a punch and not only walking away with a correct understanding of the physics, but with a visceral and intuitive sense of what’s physically going on. The explanation (theory) should be based soundly on wellestablished principles of physics, and it should be consistent and elegant. An elegant theory does not rely on bits of this concept and bits of that concept slapped together haphazardly with the intention of clearly presenting an idea. A consistent theory does not start out analyzing the momentum of a system, and then switch part-way through and begin describing the energy or force of the system. A correct theory does not use the word “force” to mean energy, and then use the word “momentum” to mean power for example. These are drastically different scientific concepts. Explanations of punching that invoke many different concepts in order to consistently and satisfactorily explain a single dynamic process are not elegant- especially when they use incorrect terminology. An author might have an intuitive idea of what he knows to be true, but if he cannot communicate that idea in a consistent and coherent manner, then it’s likely that the idea will remain inside his head. Papers and books that speak to punch dynamics exist, but usually as smaller sections of a larger treatise on a particular martial art for example. Many articles and videos found online, as well as many books, are all well-intentioned but tend to be seriously lacking in the correct use of technical terminology and in the consistent application of a unified physical model. It’s no fault of their own that many authors aren’t well trained in science and engineering, and hence tend to mix-up terms like force, power, momentum, inertia, etc. It’s an observation I’ve made that the scope and detail relative specifically to the understanding of the physics of punching is limited. I believe that most people have an intuitive understanding of many of these things, but I also believe that it is important to be technically correct and scientifically precise in usage so that the physics is preserved and a consistent theory can be applied to a seemingly complex problem. This need not require a massive display of equations either, because although the fundamental language of physics is mathematics, the engineer is also required to apply those formulas to both solve a real problem, and solve it in a way that makes sense to the rest of the world. This paper is written mainly to think out loud about my own findings and thoughts on the subject, but I hope that it will have some value to others interested in this topic.

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DISCLAIMER: If you are expecting a detailed explanation of how to punch- how to hold your arm and fist, how to twist your body or keep it straight, how to stand and move your legs, how to punch…..you will be disappointed. This paper discusses the physics and human factors of punching. It highlights principles and concepts, leaving the actual implementation of them to the reader. I have my own methods that I feel strongly about and I am still practicing them, but these methods are based on my own experience. In the end, you will have to figure things out for yourself anyway.

Basic Definitions Since this paper is about understanding the physics of optimizing a punch, the terms below are briefly defined with this topic in mind. Punch – A strike using the fist. There are many different kinds of punches embraced by many different types of combat sports, combat arts, and combat sciences: the jab, the hook, the cross, the uppercut, the reverse punch, the back fist, the hammer-fist, and the haymaker to name a few. Target – The specific site and location on a particular object or body with which you intend your punching fist to make contact. A target can be an inanimate object like the surface of a pad or a bag, or it can be the solar plexus of a moving person for example. By defining target as the surface of an object, it allows us to distinguish between simply striking the target and striking into the target. Focus – The specific site and location in space where you have the desire and intention for your fist to make contact with something. When your focus is good, you make contact at whatever point in space you desire, AND the contact occurs at a time and in a manner that maximum energy can be transferred into the target. When your focus is poor, you fail to make contact at the optimum time and place. Swing Cycle – The physical sequence of the punch as it happens over time from start to finish, with the fist moving to the target from somewhere else in space. Impact Period – The duration of time that the fist is in contact with the target. Momentum –Mass times velocity. Essentially, the weight of an object multiplied by its speed. Slow moving freight trains have very large momentum, as do fast moving small objects. I’ll show why momentum isn’t a particularly useful concept in understanding the physics of optimizing a punch.

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Force – An influence which causes or tries to cause an object to accelerate (increase its speed). Pushing or pulling an object (applying a force) causes it to accelerate, and consequently gain speed. A compressed spring applies force to an object even if the object is not moving, but the spring is trying to accelerate the object. A brick sitting on a table is experiencing the force of gravity but it’s not moving. Force is different from the principles which build off of it (energy, work, and power) in that it is a vector quantity. This means that technically you must specify both the quantity and the direction of a force. Inertia – The resistance of any object to being moved or changing speed when a force is exerted on it. It’s the “weighty-ness” of an object, but strictly speaking inertia is not mass. If you’ve ever tried to push a boat away from the dock with your arms, and noticed that it takes a while to get the boat moving, you’ve felt the effects of inertia. When you apply a force to an object that’s free to move it will begin moving immediately, but the more massive the object the more force it takes to get it up to a particular speed. When the object you are pushing on moves, you have “overcome inertia”. Energy – The capability or potential to do work. There are many different kinds of energy (thermal, kinetic, potential, etc.) In this paper we talk about kinetic energy a lot because a punch has a lot to do with movement; and the energy of movement is referred to as kinetic energy. As an interesting side-note, two fundamental principles in physics tell us that a) matter and energy cannot be created or destroyed, and b) matter and energy are essentially different forms of the same thing. Not readily applicable to punching but interesting nonetheless. Work – Force multiplied by distance. It’s energy utilized in the act of doing something. If you do work you have expended energy. If you expend energy you may or may not have done any useful work. Power – The amount of energy expended per unit of time. Large power simply means there is an ability to do work (or expend energy) more quickly. With a punch, it is more desirable to do work on the target quickly (over a shorter duration of time). This way you are delivering more energy into a target more quickly.

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Technical Principles

Force, Energy, and Work Work, a form of energy, can be defined as force multiplied by distance. If you place a spring against a wall and press it in three inches, you’ve done work because you have applied force over a distance. In the case of the spring in particular you have had to increase the force more and more as the spring deformed because that’s how springs work. If you were pushing on something else like a piece of furniture on a floor, then you’d probably push it with a relatively constant force against friction for twenty feet or whatever. You would have done work in this case too. Doing work is equivalent to expending energy, which in turn can be related to applying force over a particular distance as I just said. If you dead-lift two hundred pounds and just hold it there for an hour however, then technically speaking you’ve only done the work required to lift the weight three feet against the force of gravity but nothing more- even though you’d likely be exhausted. This is an example of how it is technically and mathematically correct to say that dead-lifting weight and holding it for an hour only represents the work done against gravity, but the overall picture seems to be missing something. It is. The rest of the story is that although the only mathematical work you did was lifting up 200 lbs. against gravity once, you are exhausted because holding a heavy weight in the air requires that you expend energy in the form of muscle contraction in your forearms, thighs, shoulders, etc. In a basic sense, work and energy are equivalent. If you do work, you will expend energy; however just because you are expending energy, you might not necessarily be doing the kind of work you are intending to do. Think about the weight lifter example. To reiterate the premise of an optimized punch, it is all about delivering energy into a target. If you do not do work on the target, if you do not transfer energy into the target which is used to cause breaking, bending, crushing, or moving- then that energy will be lost or redirected. It could be lost through heat, friction, bending of a joint, etc. If it’s lost on you, then you will feel the energy transferred back to your hand, wrist, etc. Remember that we are concerned here with transferring energy into a target, with the intent of doing damage. The idea is that energy transferred into the target will result in the energy doing nasty things inside the target like breaking bones, rupturing blood vessels and tissue, causing shock waves which disrupt nerves causing pain, etc. Any energy somehow stolen away from our punch outside the target will be energy wasted.

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What is “Power”? To understand the technical meaning of power you must first understand time and energy. It also helps to understand force. A force is easily understood by everyone- gravity exerts a force on you continuously throughout your day. It takes a certain force to slide a glass of water across a table, and a larger force to push a chair across the floor. Technically, any time a force is applied to an object, it causes that object to accelerate or at least it tries to. The object may move and have some speed eventually, but technically a force involves acceleration. There are many, many more ways to define energy however because there are so many different types of energy: chemical (batteries), potential (a rock at the top of a hill), kinetic (a moving train), and nuclear (Uranium). One thing that all forms of energy have in common however, is that in each case there is the potential to do work. Work can be defined as applying force across some distance, as we just pointed out- pushing a spring in three inches, lifting a box three feet off the ground against the force of gravity, stretching a rubber band six inches, etc. So we now understand force, energy, and work. The concept of time is obvious; it’s measured with a clock. What’s left to understand is power. Power can be defined as the rate at which work is done, or the rate at which energy is expended or transferred. If power is the rate at which work is done, then this means it can be defined as how quickly force is applied over a distance because that’s what work is. Since power is also defined as the rate at which energy is transferred, this means that it can be defined as how quickly you can transfer kinetic energy into other types of energy. If you have a powerful punch, this means that you are able to create a large force very quickly and transfer it rapidly to a target where it is converted efficiently into a different type of energy. In the case of a punch, you’d want to convert it into a disruptive type of energy which aims at breaking bones, ripping tissue, or whatever. Given this, you still might not have an optimized punch. A man who grunts and groans and lifts three hundred pounds above his head is strong. A man who can do it in only a fraction of a second is powerful. This is yet another way to understand the technical concept of power. A couple more notes about time- It’s often said that there is a “moment of impact”, but technically every event in the universe happens over some non-zero interval of time. Even a beam of light takes time to get from someone’s flashlight to your eyes. So although it seems like it happens instantaneously, and for the practical purposes of punch optimization, this might possibly be the case- the impact of the target happens over time and it’s an event, not an instantaneous moment. The repercussions of this consideration are not trivial. Again, the optimized punch is about delivering energy into a target, so this means work, which means resisting force over a distance. A moving object like a fist takes time to move through space. It takes longer to move a greater distance, which means a fist in contact with the target, continuously applying and resisting the opposite force of the target, will technically do more work and by extension- transfer more energy to the target.

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If, during the impact event, the target moves backwards away from the incoming fist under its own power, this will take away from energy that could have been delivered to the target. Lesson: the punch must reach the target and deliver energy before the target begins moving away from the punch. There is an error of thinking prevalent in some circles that you can increase the power of your punch by decreasing the time of contact, by “pulling your punch” back for example. This is only true if the amount of work done during this shorter time period is the same as the total work you would have accomplished during the longer time period. You would need to transfer the same amount of energy in a shorter period of time. Sounds interesting and in theory it is mathematically correct however, there is really no practical way to do it. It would mean diverting some of the kinetic energy away from your target-directed punch, and putting it into the muscles responsible for pulling your fist backwards. An optimized punch transfers as much energy into the target as possible. Trying to pull the punching fist back in order to reduce the contact time with the target is a waste of energy compared to the payoff. I suspect that the reason it often appears that snapping a punch transfers more energy than not snapping is that if the timing is excellent, then the muscles will relax at the precise moment when they are no longer needed. In other words, after you have done work on the target, it is no longer necessary for you to expend energy- your job is done. The thing is, the job is done at the end of the impact event and your fist will likely be experiencing a maximum force, just like the pendulum experiment. Applying force beyond this point in time is only advantageous if you are also moving the fist some distance against that force (still doing work). If you’re just applying force without moving the object at all, then you are pushing uselessly. Pushing against a nonmoving object is not transferring energy. The puncher cannot realistically control the exact distance into the target that his fist will moveonly the duration of contact. What is the optimum time of contact? It’s the time between first contact, and the point at which the puncher is either unable to push into the target more at his maximum sustainable force or his fist is not moving forward into the target anymore (doing work).

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Momentum Momentum is a very intuitive concept for most people, but one of the least useful concepts for analyzing a punch in my opinion. It is a word which is often used in articles about punching, but it can be very misleading. It is a fantastic concept to utilize for analyzing a game of billiards, but not so much for analyzing a punch. A cruise liner like the Queen Mary moving at 1 mph has more momentum than a baseball travelling at nearly the speed of light. This is of course meaningless from the interests of this paper because it doesn’t help us understand the dynamics of a punch, except to show how momentum isn’t a particularly useful physical concept here. But there are other reasons. Momentum is defined as mass times velocity, or effectively weight multiplied by speed. If we’ve defined the purpose of an optimized punch as maximizing the delivery of energy into a target, then we needed even consider momentum. After all, if we wanted to increase our momentum we would have to increase either our mass or our speed. These are exactly the same two things we are attempting to increase already, from our energy delivery perspective so there’s nothing to be gained by employing a new perspective which advocates increasing the same things. One could argue that invoking an energy approach rather than a momentum based approach to punch optimization leads to the conclusion that velocity is more important since it is “squared” in the equation (you get four times the energy for doubling the velocity), and thus to optimize a punch more emphasis should be put on increasing the punching speed and less emphasis should be put on the “mass” of the punch. I have two responses to this concern. First, it turns out from studies that very little effective mass (body weight) can be added to what most punchers are already putting into their strikes. This can be improved upon somewhat of course, but it has also been shown that the punch velocity can be improved upon significantly with practice. So in this sense, even though we’re not taking the position that a person should focus on increasing punching speed, it turns out that they do anyway- PLUS you get a “squared” effect anyway, if you choose to look at it from an energy perspective. Besides this, the human factors such as dealing with the impact period must be considered. What is a valuable lesson to learn by considering momentum has less to do with a punch and much more to do with moving things. In this sense, if you’re purely concerned with moving a body, or knocking something out of the way, then momentum is your concept to deal with. In that case, little guy hit big guy fast makes big guy move slow. Big guy hits little guy fast, makes little guy go really fast. In punch optimization you’re going to be trying to maximize speed anyway, and momentum is usually a sidetracking concept.

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Before leaving the concept of momentum behind, let’s look at an enlightening demonstration. It’s an interesting use of side-by-side comparisons of momentum principles with kinetic energy principles. This Physics 101 demonstration involves a gun and a log. A small caliber rifle is fixed to a bench-top and loaded. A 50 lb. log or block of wood is suspended from a frame so it can swing back and forth along the axis of the log like a battering ram (not like a child’s swing set). The log is positioned a foot from the end of the gun barrel and the rifle is fired. What you notice is that the log is pushed up a little bit and begins swinging gently, presumably because it was hit by the bullet. The demonstration is setup so that the bullet embeds itself into the log at impact. One thing that the physics student is supposed to appreciate about this demonstration is the fact that the kinetic energy of the moving bullet is transferred into kinetic energy of a moving log. The student is also supposed to appreciate that the momentum of the bullet is transferred to the momentum of the log. Now, in general momentum is always conserved- meaning that the mass of the bullet times its speed is always going to equal mass of the log (plus the embedded bullet) times its speed. The bullet is tiny but fast, whereas the log is heavy but slow (when struck). There are many more technical details involved here beyond the scope of this paper such as elastic and inelastic collisions, and the fact that energy is always lost during a collision in the form of heat. There are several important things to take away from this experiment as it relates to optimizing a punch however. First, firing a bullet at something is not a very effective way to move a heavier object. It would have been better to walk over and lift the log up by hand. The second thing to appreciate relative to this paper’s topic is that a bullet is good at delivering energy into target. It’s damn good. Now try this thought experiment: Take a small, one inch thick steel plate with a front side surface area about the same as your fist, like four inches by four inches. Then, hold the steel plate over your chest and have someone fire off a .45 caliber bullet right at the plate you’re holding. What you are guaranteed to find is that there would be a surprisingly small force experienced. Sure we’re ignoring things like muzzle flash and the deafening sound and the danger of ricochet but it’s very important to understand what is going on with regard to momentum and energy. Remember that the fifty pound log barely moved, and you likely weigh more than fifty pounds (and hopefully the bullet is not embedded in your torso). Now here’s something that is astonishing to most people: It’s possible for a man to punch with the same kinetic energy as a round fired from 9mm handgun.

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And here’s the mathematical proof: The kinetic energy of the 9mm bullet, with an 8.5 gram bullet moving at 360 meters per second is 550.8 Joules.

Bullet:

The kinetic energy of a fist, with a 20 lb. “fist” (assuming we’ve practiced putting some weight of our arm and body behind the fist), moving at 25 miles per hour is 551.9 Joules. About the same energy as the bullet.

Fist:

The figure 25 mph was taken from a recent engineering study of a British boxer’s punch, showing his average speed to be approximately 25 mph. Consider that although our boxer clocked a punching speed of 25 mph, according to The Guiness Book of World Records the greatest reliably recorded speed at which a baseball has been pitched is 100.9 mph by Lynn Nolan Ryan (California Angels) at Anaheim Stadium in California on August 20, 1974. This means that Mr. Ryan’s hand was moving at least 100 mph. If a man can move his hand four times faster than our example and somehow manage to sustain the force at impact without much energy loss, then it’s at least theoretically possible to punch with more than ten times the kinetic energy of a 9mm round.

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If you can punch someone with the energy of a bullet, why isnâ&#x20AC;&#x2122;t a punch in the gut always a deadly action? The primary reason is simple and gets back to the definition of the optimized punch. The bullet is transferring all of its kinetic energy into the target, and you with your punch are not. There are some technical details such as the fact that your fist has a surface area roughly one hundred times that of bullet (see below). This makes transference of the kinetic energy of your fist into the target enormously challenging if you try to do exactly the same thing that the bullet is doing; however nobody ever said that your fist had to physically enter the target in order to transfer its kinetic energy into the target.

Surface Area Bullet:

Fist:

Transfer of energy into the target can also happen through a medium, much in the same way those little ball bearings on business executivesâ&#x20AC;&#x2122; desks show how one ball can swing and hit a bunch of ball bearings lined up, but only end up with the bearing on the end swinging up. Wiggle a rope at its end and the other end of the rope swings soon after. Wiggle the rope very quickly, and the end of the rope whips with a snapping sound and breaks the sound barrier- roughly 700 mph. A medium can be a very good ally. Velocity is important not because this is acceleration (itâ&#x20AC;&#x2122;s not), velocity is important because the faster your fist is moving, the larger the deceleration you will be able to see when your fist slows down. A fist slowing from 27 mph to zero in 0.1 seconds has more deceleration than the same fist slowing from 18mph to zero over 0.1 seconds. More deceleration or acceleration means more force. Your fist slowing down quickly is decelerating, and a faster fist decelerates more (assuming the impact events are over the same duration of time). In my opinion, there are never really more than two fundamental technical things to consider in a punch: How much kinetic energy is available? and, How much of the energy is being used do to work (transfer energy into the target)? These are the two most critical questions to ask about any 16

punch. There are however, a multitude of human-factor questions which are also important but these two are the most revealing physics-based questions to consider. In the case of our professional boxer, it turns out that he is hitting faster and with far more force than the average Joe to be sure. He is generating more kinetic energy because of his faster speed, and he likely has more mass involved in the punch than the average Joe. According to the instrumentation he is producing 880 lbs. of force “instantaneously”, meaning over a very small time interval. It is also extremely likely that he is not losing much energy during the impact event by rigidly sustaining the reaction force. In this case (and in many similar studies) we’re not told what the distance is through which he is supplying this force, and I’d venture a guess that it wasn’t measured. It’s complicated anyway and difficult to measure because of gloves, padding material, target material, etc. If the boxer makes contact but his fist only moves into the target a few millimeters, it is unlikely to do much damage because this is essentially skin deep. Of course we can assume that this boxer has no intention of stopping skin deep, he’ll likely drive the punch as far in as he can, causing plenty of damage. On a hard plastic test pad with sensors, it’s not possible to punch deep into the target so extrapolation to human bodies must be done carefully. This is an interesting thing to consider however. If you want to optimize a punch it isn’t enough to just generate kinetic energy, and it isn’t enough to be able to exert force. You must supply kinetic energy, and then efficiently use it to do work on the target by exerting force over a distance. What does it mean to say “Hitting with force”? And what’s this all about? Remember how force is defined. Force is the influence which causes or tries to cause an object to accelerate. Slowing down is also acceleration, it’s just negative- some call it deceleration. As a punch reaches the target and makes contact, the effective mass of your punch (which may include fist, arm, and some body weight) begins to decelerate (negatively accelerate). This negative acceleration of mass is the force you experience pushing back on your fist and perhaps into your own body through your appendages. The duration of time over which this force of your decelerating fist occurs is what allows work to be done on the target. However, in order for work to be done on the target the fist must apply force over distance not just time. Now, it’s likely that your fist will be driving into the target for some distance, but this is not the technical goal. The technical goal is to apply force over distance with the constraint that it must be done quickly to avoid overcoming inertia of the larger body. To deliver energy into a target your punch must be fast enough to capitalize on the target’s inertia, and you must apply force over distance in order to effectively do work on the target. Applying force can be done either structurally, passively by deceleration of mass, or by some 17

combination of the two. Effectively doing work on a target requires that you deliver a sufficient supply of kinetic energy to the target.

Gravity Every person walking around is subject to the force of gravity at all times. If you jump off a tall building you’re subject to gravity even in free-fall. You’re experiencing weightlessness as you accelerate (onto the street). In a vacuum, without wind resistance, all objects fall at exactly the 20

Geometry Straight vs. Curved A free-body like a cube in space has only two possible ways it can physically move: It can translate and it can rotate. Translation means moving from point A to point B along a straight line, while rotation means spinning about an axis. These are very different types of motion. Any motion in the universe is either translation, rotation, or some combination of the two. When it comes to the punch, one can find different types of punches which involve primarily one or the other of these two types of movements. For example, the ‘jab’ in boxing involves throwing the lead hand straight out to its target (although there is some body rotation involved even here). The ‘hook’ on the other hand, involves more twisting of the body and delivering the punch from a rotating body frame. No method is purely translation or purely rotation, but some methods use a higher percentage of one or the other. 21

The reverse punch in karate is a good example of a punch which is predominately translationmoving straight forward with the body and fist. The roundhouse kick in karate is a good example of a strike which is predominately rotational in nature. Both types (translation and rotation) involve moving masses and hence, kinetic energy. The exact formulas for calculating the kinetic energy in each case are different, but they are fundamentally similar in that you simply have moving masses with kinetic energy. Now you might think that it would be possible to add the energy of your linear translating fist, with the energy of your rotating body somehow to get an extra boost of kinetic energy. This is correct in theory; however it is extremely difficult to move the body in this way- to maintain the kinetic energy of rotation while you transition into a purely linear strike. It entails translating the kinetic energy of rotation into a linear motion through a series of changing the muscles involved, and then adding to it from there. I believe that while this may be theoretically possible, there are far better ways to spend one’s time optimizing punching power.

Lines and Angles If we assume that the applied force is continuous through the swing cycle and the impact period, then the direction of force application should be considered since force is a vector quantity. How frustrating is it when you pull your office chair away from your desk and the arms get stuck under the desk? This is certainly not the optimum direction of force application for moving your chair. Incorrect direction of force application is another way that you reduce the work done on the target. Your muscles contract and relax in such a sequence as to direct a maximum amount of force in a certain direction, depending on the position of your body, hand, shoulder, hips, forearm, etc. If you do not take advantage of this, then the energy of your punch will be reduced. Force for a punch is directed along the lines of your appendages to conclude at a specific point in space for optimum energy. To optimize your punch, make sure that the target is at that point in space. This idea of applied force direction goes hand in hand with the consideration of energy loss through bending joints. When lines are straight and when maintaining those straight lines is done effortlessly, then joints bend less. However, it’s also important to consider 90° angles as well, since this is an angle that, like 0° and 180°, can be kept from bending much more easily.

A very important take-away from this is that if the direction of applied force of your punch is not exactly perpendicular to the target, then there will be energy lost. Remember that force is a vector quantity; it has a value and a direction. The maximum force of your punch during impact might be 1,000 lbs. but is all of that force directed precisely straight into the target or is it cocked 22

a little with some force directed off-angle? Just because you hit a flat surface doesn’t mean that you are hitting it perpendicular.

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Focus Humans are psychological creatures, not robots. This means that even though a person has an intention to do something, they may be unable or unwilling to do it. Focusing means selecting a target and punching that target. Now, as with other things, there is more to this than meets the eye. A powerful punch means that a maximum amount of energy is delivered to the target. Pulling back, extending the arm, punching...at what arm position exactly, and at what point in time should you make contact with the target so that you punch is optimized for power? Focus is 25

about understanding the optimum location of the target relative to where you are, and where your own body parts are. Imagine releasing a pendulum to swing freely from left to right. At the moment it is released it is at a standstill. From that point it quickly gains speed until it is moving as fast as it ever will- at the very bottom. After the weight passes the bottom position and swings to the right, it starts to slow down against the force of gravity and the kinetic energy is transferred to potential energy once again. What does this have to do with an optimized punch? Alot. Imagine that you had a twenty five pound steel pendulum hanging from a ten foot rope, and you released it from a height of five feet. Watch it swing and imagine trying to stop the swinging pendulum right as it passed the bottom most position, where it was moving the fastest- a difficult if not painful concept. Now imagine catching it and stopping it much closer to its highest position, near where you released it- much easier and painless. This simple thought experiment illustrates how critical the position of a moving body is relative to its dynamic energy transfer cycle (potential to kinetic) if you wish to maximize kinetic energy. Itâ&#x20AC;&#x2122;s trivial to say that you must hit faster to hit with more power- this is fairly obvious by now. To optimize your punching power however, you must learn exactly when in your punching cycle to make contact with the target. In other words, you must know the exact position in space where your fist has maximum kinetic energy and make sure that your fist and the target are both there at that position at exactly the same time. The golf swing is an excellent example of how a surprising amount of energy can be delivered to a golf ball with very little effort on the part of the golfer, provided the golfer has superior technique. Itâ&#x20AC;&#x2122;s also a great example of how trying to add energy by swinging harder or faster too soon in the learning process usually fails for the amateur. When the amateur tries to swing faster, it more often than not results in a poorer quality technique. What this means fundamentally is that the focus is worsened, the transmission of energy to the ball is reduced, the angle of impact is skewed, and the structural integrity of the body frame is compromised. Developing superior technique can allow the golfer to impart energy to the ball with very little expenditure of his own energy, since the transmission of energy is efficient. The weekend hacker often needs to make up for precise energy transmission by imparting excess energy of his own. With superior skill, the level is reset and the professional golfer can begin to add more and more of his own energy on his swings since he is always able to keep the energy channeled efficiently from his body into his target (the ball). This concept has been proven in scientific studies of Olympic boxers and karate practitioners. The more skilled athletes are able in their punches, to impart more force. And not surprisingly, heavier boxers tend to hit harder than equally skilled boxers because the small percentage of effective body mass they are using is just larger. As for delivering energy into a target, consider that the puncher cannot realistically control the exact distance into the target that his fist will move- only the duration of contact. What is the optimum time of contact? Itâ&#x20AC;&#x2122;s the time between first contact, and the point at which the puncher 26

is either unable to push into the target more at his maximum sustainable force or his fist is not moving forward into the target anymore (doing work). An ideal puncher stops Follow Through The purpose of “following through” in general, is to prevent you from stopping the focus of your impact short of where it should be. An optimized punch delivers energy into the target, so the focus should usually be inside the target and not the surface of the target. Notice that I said “usually”. Caution should be exercised here because focusing too far inside the target, or even past the target could position your appendages in such a way as to lose kinetic energy upon impact due to joint flexing, etc. Plus, your focus must take into account the swing cycle of your punch so that at impact you have reached maximum velocity given the various other constraints. Following through helps maximize the kinetic energy of your punch by preventing disruption in the swing cycle. Stop short by not following through and you lose energy in two ways: you lose energy because you slowed down your punch prematurely, and you lose energy because while you were slowing your punch down you were expending energy in superfluous muscles. This is another reason why moving targets are so difficult to hit with maximum force. Making contact with the target only two inches off form the optimal focus point will reduce the kinetic energy of your punch significantly.

Making Sense There have been TV shows like National Geographic’s Fight Science which have talked about the “physics of fighting”. There are some amazing graphics to be had and a lot of money was spent to measure the force, speed, and displacement of various dummies, pads, and bags. This is unfortunately (in my opinion) more theater than true science. It tells us a little bit about a lot of things, but with very little depth and by means of an inconsistent perspective. According to many shows like this, the maximum ”force” of a strike is the be-all, end-all of punching capability. It’s also confusing because they tell you a little bit about what is happening, but very little about how it is accomplished. More infotainment than information, things are showcased which everyone in martial arts pretty much already knows. But even there, it’s extremely limited presentation or even examination into the details, often fails to reveal and uncover the fundamentals of the physics as it applies to optimized power delivery- keeping human capabilities in mind. As an example, from one fight science show by National Geographic, they say “Boxer Steve Petramale delivered about 1,000 pounds (453.6 kilograms) of impact force, the equivalent of 27

swinging a sledgehammer into someone's face.” Really ? Swinging a sledgehammer into your face at what speed? Questions like this are important, as is the nature of the interface, and the materials. Getting hit by a slow moving sledgehammer wrapped in thin foam is much different than getting hit by a fast-moving hammer unprotected. Likely, uncovering details like these is not something fit for television. Also reported on one show was that the Muy Thai kick generated the “impact of a 35 mph car crash”. What the hell does this mean? Does this mean that getting kicked by a Muy Thai fighter is the same as getting hit by a car at 35 mph? This is ridiculous because a car travelling 35mph can easily break off a fire hydrant at its base. Can a human being kick a fire hydrant and have it break off at the base? No way. These statements are meaningless in my opinion. More people likely have an intuitive grasp of things like force and momentum, perhaps that’s why they are used so frequently albeit often incorrectly. Momentum isn’t useful as a gage of punching power because it assumes you want to transfer momentum from you to your target. No. You want to transfer energy. I mean, yes of course you will be transferring momentum somehow, that’s undeniable. But it isn’t something that we can easily grasp when analyzed form the perspective of a punch. Football players and momentum? Now that makes sense. Getting tackled means moving your body toward another body, joining and then moving together. That’s momentum transfer. Energy is used to do work, like break bones and disrupt tissue, it’s just a different way to think about the process, nature happens no matter how we humans choose to interpret it and look at it and classify it. So we might as well look at it in a way that makes consistent logical scientifically correct sense. To recap, a large momentum can come from a big ship moving slowly at a dock, or a small bullet speeding through the air, or a linebacker slamming into you but it’s difficult to use this concept for analyzing a punch. Don’t get thrown off the path of comprehension. To get more of an intuitive grip on momentum and energy, it’s worth taking a look and comparing the momentum of various items with each item’s kinetic energy. Try to imagine what it would feel like to be hit with these things at their listed speeds.

Projectile Baseball Ford Explorer 9mm Bullet Cruise Liner Baseball

Mass 0.15 4,053 8.5 136,363,636 0.15

Velocity kg lbs g kg kg

90 5 450 1 671,000,000

mph mph m/s mph mph

Momentum (kg*m/s)

Kinetic Energy (J)

6 4,118 3.8 60,960,000 44,994,576

121 4,602 861 13,625,779 6,748,372,898,065,920

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A major league baseball pitcher might be able to throw a ninety mile per hour fast ball at you. If it hits you in the stomach and you’re ready for it, it’ll probably hurt a bit but it certainly won’t kill you. The 90mph baseball has a momentum of 6. (I’ll leave off units here to keep it simple. Also, even though some velocities are given in English units I’ve already converted to get the correct momentum and energy.) A 9mm bullet fired at your gut however, likely will kill you, or at least put you in the emergency room. The momentum of a 9mm bullet fired at you? 3.8- nearly half the momentum of the baseball. This shows that looking only at the momentum is not a reliably safe method of determining lethality. The kinetic energy of the bullet in this case is more than seven times the energy of the baseball. And to show how looking only at the kinetic energy of an object isn’t enough, consider a slow moving SUV. The Ford Explorer moving at 5mph has a momentum of 4,118 and a kinetic energy of 4,602. Very high numbers indeed, but you don’t usually see people being rushed to the hospital after being ‘bumped’ by a car moving at 5mph in the parking lot- especially considering the much higher numbers. And to really hammer home the point, take a look at a cruise liner like the Queen Mary traveling at only 1mph versus a baseball traveling at close to the speed of light. Clearly a ridiculous scenario, but it shows that these two objects have similar momentums with the ship a little higher. The baseball rocketing through space has a lot more kinetic energy. So both momentum and kinetic energy are valuable tools, and each has a place in analyzing physical events. It’s just that sometimes it’s clearer to understand an event using a momentum approach, other times an energy approach. For punch dynamics, I don’t think it’s helpful to look at momentum.

Conclusion If you’re interested in increasing the power of your punches you can practice more and train harder; but rarely do we take time to stop and think deeply about precisely what it is that we’re doing or what we’re trying to do. Having developed a single principle of doing work on a target, from an engineering and physics based perspective we can then begin to start asking ourselves if what we’re doing falls more in line or less in line with this principle. There are no secret techniques- only proper utilization of the human body and mind to move precisely along and within a selected subset of physical laws to generate, deliver, and transmit energy into a target with minimal effort. Invoking dozens of different concepts and physical laws clouds the issue from its simple beauty. To be precise and consistent we must a have both a 29

scientifically correct and intuitively deep understanding of the physical process, and we must use words consistently and correctly to communicate ideas effectively. Those who can grasp the principles of the punch dynamics will be able to more effectively implement them into their own systems and training styles, rather than gaining ground more slowly by rote memorization or simplistic copying of a coach or instructor. Groundbreaking for me, but perhaps uninteresting to others is my conclusion that a punch can basically be done executed effectively in only one of two ways (or some combination). You can apply force in a punch either actively or passively. By this I mean that you can be active in using your muscles to push through into the target, or you can allow the mass of your arm to decelerate into the target on its own without any muscular effort. Work needs to be done on the target. The work is done only through producing a force across some distance. This application of force happens over some short period of time. The application of force can happen either actively- by applying a force through structural biology; or passively through deceleration of your punching mass. When deceleration of your punching mass occurs, energy can be lost through elastic deformation of joints, etc. Almost always the punch is some combination of these two methods. When it’s not, when it’s almost purely one or the other… that’s very interesting and I continue to learn from these cases.

Appendix Mass vs. Weight Strictly speaking, mass and weight are two different things. Most people use the terms interchangeably, and for everyday situations here on earth there’s rarely any need to distinguish the two except for clarity. The technical difference between mass and weight is that mass is the same whether you are on earth, on the moon, or in deep space. 50 kilograms is fifty kilograms. On Earth, fifty kilograms exerts a downward force of (50 kg.)x(9.8 m/s2) = 490 Newtons. The figure 9.8 meters per second per second is the acceleration of gravity due to gravity on Earth. On a different planet, the force due to gravity is different even though it’s the same 50 kilogram mass. In this scenario we dealt with metric or “S.I.” units. The same scenario can be had in our more familiar English units. A 200 lb. man is 200 lb. on Earth but not on the Moon because 200 lb. is a weight, not a mass. The 200 lb. man on Earth has a mass of (200 lb.)/(32.2 ft/ s2) = 6.2 Slugs. What the hell is a slug? Yeah, it’s one of those old-fashioned terms that is almost never used. But it is also fine to just use the term “pounds” for both mass and weight as long as you’re not an engineer trying to launch rockets. Just keep in mind that that there is a difference between the mass of an object and the force that object exerts due to gravity. Some systems and some 30

people use the terms ”pound-force”, and “pound-mass” to clarify whether they’re talking about mass or weight.

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Pondering the Punch

Finally Grasping an Intuitive and Scientifically Correct Understanding of the Physics of Striking