The Weekly Warfare   Musings martial from across the SCA

(Ed. This is part 4 of a multi-part series. Comments that indicate a failure to read previous entries shall be mocked and, possibly, moderated with extreme prejudice. The author took the time to do the research, you can take the time to read it)
(Part 1 Part 2 Part 3)

In the previous articles, I described the amount of force necessary to cause a concussion (Part 1), the force levels from a typical blow (Part 2), and other sources of force that can contribute to concussions (Part 3). In part 4, I will describe a set of techniques that will help you to both avoid concussing your friends and avoid being concussed yourself. Fortunately many of these techniques are also important aspects of good fencing in general. They will largely focus on the core mechanics of your fencing and will generally require active practice in order to put into regular use.

How not to concuss your friends:

The number one way to prevent concussions is to minimize or eliminate blows that land hard enough to cause a concussion. As the person delivering the blow, the key to keeping yourself from concussing your opponent is having control over your own weapon and body. Maintaining this control is largely a matter of practice; however there are certain techniques that will make it easier to keep control over your motions, and you should focus on using these techniques. First and foremost,Train good technique regularly. It is important to practice such that your technique is good even when you’re tired. Furthermore, consistency is a product of practice. If your lunge varies wildly in its length, how can you possibly have any idea how hard you’re going to hit someone who is standing within that range?

In general, you should hold your body upright and keep your arm and body relaxed and flexed, not tensed. You should also keep your core musculature engaged, tuck your tailbone, and support yourself with your legs planted firmly on the ground.

When you are moving, you should push yourself with your legs. Move forward by extending your rear leg and move backwards by extending your front leg. Your shoulders and hips should remain parallel to the ground and shouldn’t rise or “bounce” when you move. Likewise, don’t “fling” your body weight into the motion and allow the rest of your body to follow. In both of these cases, you are engaging in a motion where you spend a period of time falling and where it is impossible to control the placement of your body weight. Maintaining this safe technique is largely a matter of keeping your tailbone tucked, your core engaged, and taking small steps.

When striking your opponent, you should be certain to extend your arm completely before the rest of your body moves (without locking your elbow). If your arm is still in the process of extending when you strike your opponent, it is impossible for you to adjust or cushion the blow if needed.

As with your footwork, it is also important to push your sword forward rather than punching with it. Your movement should be similar to a waiter extending a tray. Punching and flinging motions are more likely to result in a hard hit because they offer less control over the muscles that are recruited. These motions also strike with a lot of impact force (i.e. with a “pop”), which makes it less likely that the sword will flex. Wistric recently suggested bare-knuckled lunges (with your fist rather than a sword) against a brick wall as a method for testing this mechanic. If this idea gives you pause, then it is likely that you lack control over your technique. If it hurts,then your technique is unsafe (and you’re hitting your opponents that hard over an even smaller cross-section. How do you think that makes them feel?).

Cuts should be delivered from the wrist, shoulder, or a sequential combination of the wrist and shoulder (only one moves at a time), not the elbow. This is better technique for a variety of reasons, however from a safety perspective, this prevents the kinetic linking that is typical of blows from armored combat (but is wholly unnecessary for cutting with a sword). It is important that you avoid using your hips when you cut.

Once the arm is extended, reaching your opponent should be performed by moving the body and/or legs. These motions should also be performed by pushing yourself forward. Do not jump.

If necessary, you should begin cushioning the blow immediately after impact (If you are striking with a technique that causes it to be necessary to cushion before impact so that you don’t hit too hard, you need to re-read the section on how to strike). As noted above, this will be impossible if you are tensed or if the arm is still in the process of extending.

It is best to cushion thrusts by withdrawing the arm in a straight line past your body (i.e. by reversing the motion of the extension). This method will provide the greatest range of motion for cushioning the thrust and removes the weapon from its position between you and your opponent where it can become grounded on your body. Other methods of breaking the force of a thrust such as releasing the ring and pinky fingers and breaking at the wrist in order to carry the weapon down or to the sides can cause the pommel to land ground itself onto your leg or chest which can result in an extraordinarily hard hit if your opponent is falling, slipping, or completely fails to control their body movement. While these situations may not arise due to your actions, you still have the ability to prevent their injury and should do so if possible.

Cushioning cuts is simply a matter of breaking the motion at a joint. The best ways to break a shot are by releasing your pinky and ring finger or by breaking at the wrist. These this will limit the mass behind the impact to only that of the sword and hand. This smaller mass should be less than the mass of the head and so due to the relative difference in inertia, it is the weapon rather than your opponent’s head that will undergo acceleration due to the force of the blow. In situations where breaking at the wrist is not possible, breaking the impact at the elbow or shoulder should be sufficient.

As fighters, it is also worth considering that there are sometimes blows that you shouldn’t throw even though it would be legal to do so. This is largely a matter of judgement and it is worth considering that it will sometimes be very hard to override your competitiveness in order to protect your opponent’s safety. These situations may occur for a variety of reasons. For instance, if the ground is slippery, you may need to refrain from lunging because you can’t be certain of how you will land. It may also be prudent to change how you target your blows such that you avoid hitting people in the “danger zones” for causing a concussion or to be gentler when striking these areas. For instance, in melees, it might be best to avoid blindsiding someone with a thrust to the temple, even though it isn’t against the rules.

As Marshals/Instructors:

The above list is somewhat convoluted, and not all of the techniques can or should be enforced by the marshallate. However, there are a couple key mechanics that marshals should keep an eye out for. Ultimately fighters who routinely:

1) Punch with the sword
2) Fail to extend their arm completely before moving the rest of their body
3) Throw themselves forward or jump at their opponent
4) Fall down or slip
5) Use their hips to generate force on a cut

Should be targeted for correction. These fighters are a danger to others and, if they refuse to alter their mechanics to correct these problems, they should be removed from the field.

How not to get concussed:

While it is important to understand that the blame for a hard shot generally lies with the person who is delivering the blow, there are a number of techniques that allow the recipient of a blow to do so more safely. Because of this, it is worth considering that a fencer who consistently fails to perform these techniques is a danger to themself.

Awareness – Fencers should be aware of when they’re about to be hit, especially in melees. Fighters who can’t see shots coming cannot protect themselves from injury and should be removed from the field.

Brace for impact – When a fencer knows that they are about to be struck in one of the danger zones, it is possible to brace for impact. This can be done by pushing their head into the blow with their neck muscles and by tucking their chin. Importantly, this is an active use of the neck muscles: Do not tense.

Keep your eyes open – Train to keep yourself from uncontrolled “flinching” at moment of impact and keep your body relaxed. Never turn away from a strike, as this exposes parts of the mask not designed to take a shot.

Maintain good muscular tone in your neck – Your neck muscles are the primary method of resisting impacts. When you are fighting, you should maintain good muscular tone in these muscles so that you can resist impacts even when you are surprised. This is difficult to accomplish, as those who lack body awareness will be incapable of even feeling what this is like. Fighters should engage in routine exercise and practice until they are capable of this. Fighters who are frequently “bobble-headed” are generally failing to do this.

Defend yourself – Don’t rush your opponent without defending yourself. Carefully evaluate how you are performing your “heroic sacrifice to take out the MoD” in melees.

Avoid “bouncing” footwork, “flinging” your body forward, and “jumping” when you lunge. You will be unable to control your body during the falling portion of these actions and if your opponent strikes you during these motions, your body weight will add significantly to the impact force.

Wear a mask that fits – Many fencers have masks that are too large. A correctly fitting fencing mask should result in a slight change of voice pitch. A mask that is too large may in some circumstances, act as an additional lever and make a concussion more likely.

Improve your level of Fitness – There are numerous risk factors for concussions that are related to general health and well-being. Smoking, high blood pressure, obesity, unmanaged diabetes, stress, dehydration, and age all place you at an increased risk for receiving a concussion (Because these result in your brain shrinking slightly such that it has more space to bounce around inside your skull). Some of these can’t be helped (you’re not getting any younger), but if you’re worried, you should take care of your health, stop smoking, engage in routine exercise, practice hydrating, etc.

Wear a mouthguard – There is some evidence that mouth guards may provide a slight protective effect against concussions for football players. Mouth guards are cheap and might not be a bad idea if you are particularly prone to concussions or getting hit in the face.

Do not tolerate dangerous technique – Leave a paper trail when bad things happen. If a same fighter is consistently a problem, deal with them mercilessly. Be aware of your kingdom’s marshallate procedures and policies. If you diverge from procedure, your KRM may be unable to take action.

As Marshals/Instructors:

Recognizing fighters who are placing themselves in danger is perhaps even trickier than identifying fighters who pose a hazard to others. In general, marshals should look out for and attempt to correct fighters who frequently:
1) Charge without defending
2) Throw themselves towards their opponent
3) Are surprised by being hit
4) Freeze, Flinch, or otherwise tense their body before impact
5) Receive hits like a sack of potatoes (i.e. fail to actively resist hits)
6) Are “bobble-headed” by face and chin shots

This past Saturday I taught a class on drills (and other ways to improve) on your own and with a partner. My notes are below, and the drills covered are linked here. One day I should get video of these.

First, GOOD DRILL PRACTICE:

• Don’t try to win the drill (ffs!). If your job is to get hit, you get hit. Practice the action.
• Start slow and large, train up to small and precise. 80% success rate (4 out of 5). If it’s below that, go slower and larger. If it’s above that, smaller and faster.
• Targets should be small (hand, not chest)
• Add footwork when it gets too easy.
• Drill for 15-30 minutes at practice. If you have a two hour practice, this still leaves an hour and a half for fighting. Fighters will just get bored after 5 minutes or so, so alternate drilling different actions (feel free to cycle back to the first drill). Add time for conditioning on top of the drill time.
• Execute an action until it can be done consistently before moving on to the next.
• If you’re the coach, take this time to work on your form. Make sure your en garde stance is solid and your footwork and sword-work are clean.

Solo Drills:

Lunges

• Go slow to go fast. Train at Tai Chi speed to develop the muscle memory. Don’t train going as fast as you can. Train doing it right.
• If you’re missing, your hand is going after your foot (point control is a myth).
• I use a target of four small pieces of duct tape. One for each shoulder, the face, and the torso at “en garde” height. Start with just hitting one, then just hitting the next, and so on. Once consistent, start rotating through the targets or randomizing them.
• Break it down into separate pieces: Start with the extension to strike. Step back half a step to add in the extension and shoulder rotation. Step back another half step to add in the torso lean. Step back another half step to add in a small lunge step. Step back another half step to go train the full lunge. Again, repeat each step until it can be done consistently before moving onto the next. Start over from the beginning each day.
• Falling into a rhythm of lunge/recover/lunge/recover is bad. Don’t do it. I recommend using the Random Timer app for your smart phone if you have one. Set the interval to beep between, say, 3 and 6 seconds. Lunge when it beeps. Recover when it beeps again.

Conditioning

• The next best use of your solo time is working on your conditioning: Develop the fast twitch muscles of your arms and legs (the ones responsible for bursts of energy), work on your core strength so you can stay in guard a long time, and cardio. These can be worked with mostly bodyweight exercises, no gym needed. Look around for examples (or maybe Dominyk can post some links here).
• Also, Hell Drills. Misery loves company, so try getting your whole practice to do these.

Dead time training:

• We have a lot of dead time in our lives. Use it to train.
• Do footwork around the house instead of normal walking. 
• Practice standing in guard in line, waiting for the shower to warm up, on telecons, whatever
• Hold your sword extended out to the side at shoulder level while watching TV.

Paired Drills:

• Glove drills
• Priest Drill
• Drill of N-things

Drill building:

“I want to be able to do a thing.” Drill doing that thing. Literally, “My dagger parries to the high inside line don’t work.” Have somebody lunge at your left eyeball until you can parry it effectively. Then add footwork (you or them leading the footwork). Have them add a setup (feint to the low-line, sword beat, whatever). 

If you can’t find anybody to drill with you, do directed sparring: Drill doing a thing against an opponent who’s actively resisting (because they don’t know what you’re working on). You will eat a lot of sword until you get it right. Ego impedes improvement.

(Ed. This is part 3 of a 5 part series. Comments that indicate a failure to read previous entries shall be mocked and, possibly, moderated with extreme prejudice. The author took the time to do the research, you can take the time to read it)

(See Part 1, Part 2, Part 4)

In the previous two articles, I demonstrated how the typical amount of force delivered by SCA rapier thrusts relates to the force required to cause a concussion. Importantly, the levels of force delivered against Llwyd’s machine (~15-28lbs) were significantly lower than this threshold (~100lbs). However, we know that concussions do occur from blows delivered in SCA fencing. Consequently, we must therefore conclude that these blows are either delivered with an atypically high level of force, that Llwyd’s machine is not measuring typical blows, or that there are other factors that add to the amount of force delivered in order to reach this threshold. Here we discuss those other factors which include the angle and location of impact, the body movements of the fencers, and the technique used to deliver the blow.

Impact Location and Direction:

The largest factor that determines whether a blow can cause a concussion is where and how it lands. Obviously a blow that doesn’t strike the head won’t cause a concussion, but where a blow lands on the head is also important for determining whether the head undergoes linear or rotational acceleration. As we showed in the first article, far more force is required to cause a concussion due to linear acceleration (~750 lbs) whereas rotation can cause a concussion with far less (~100lbs).

Figure 1: Target areas on the head that are most likely to cause a concussion. Image adapted from The Passive Fist (2010). The Squared Circle Blog. http://thepassivefist.blogspot.com/2010_05_01_archive.html

As shown in Figure 1, the blows that are most likely to cause rotational acceleration of the head include rising blows landing under the chin, rising blows to the top of the forehead, and cross-wise shots landing on the cheeks or temples. These blows are more likely to cause rotation of the head due to the asymmetrical shape of the head and the placement and shape of the neck muscles that resist this kind of motion. Specifically, the shape of the head means that the face is further from the axis of rotation than the rest of the head, which provides a longer lever arm for blows to act upon. Likewise, the muscles that resist this kind of motion are the sternocleidomastoid which is relatively small and is not directly aligned to oppose this kind of motion.

Figure 2: Location of sternocleidomastoid muscle. Image from Wikipedia.

Body Movement:

The second biggest factor is likely the body movement of the fencers. The blows discussed in the second article were measured against a stationary machine under relatively “perfect” conditions. During a bout, fencers are typically moving and they may accidentally put their body behind blows by using poor technique for delivering a blow such as kinetic linking (i.e. throwing a rattan blow), flinging their body forward in their footwork, jumping, or falling (See Figure 3). Importantly it is possible for either fencer (the blow deliverer or the blow recipient) to add force through body movement.

Figure 3: By throwing his body into the air, Wistric is adding a lot of force to the impact he’s about to receive when he lands on David’s sword. Image from Wistric’s Facebook.

The relative contribution of body movement should not be underestimated. Consider how much force is generated by a person walking into a wall. If that person’s mass is 100kg and they were walking forward at a pace of 1m/s (a moderate walk), then we can calculate this amount of force as long as we know how long it takes their body to stop (i.e. the amount of force is reliant on the rate of deceleration). Due to Newton’s third law of motion (When one body exerts force on another, the second body simultaneously exerts an equal and opposite force on the first), when you collide with the wall, it exerts an equal and opposing amount of force on you, which causes you to stop (i.e. decelerate). Therefore, the faster you stop, the harder you hit the wall (Assuming the wall doesn’t move). Consider a relatively slow stop, taking 0.5 seconds; we can calculate the force as F = 100 kg * 1m/s/0.5s = 200N ~50 lbs. In contrast, a relatively fast stop, taking 0.1 seconds, would result results in F = 100kg * 1m/s/0.1s = 1000 N ~250lbs. Based on this, it is easy to see how movements of the body can dramatically increase the force of impact that can occur well beyond the forces measured by Llwyd’s machine.

Punch vs. Push:

Another factor is the temporal characteristics of the impact. The muscles of the neck provide a significant level of protection against concussions because they are able to resist rotational movement of the head. However, these muscles need to constrict in response to an impact, which takes time. Because of this, impacts that cause force to be applied faster are more dangerous than impacts that spread that force over time, regardless of whether the total force or the maximum force is higher in the slower impact. For instance, a “punching strike”, which maximizes impact force is more dangerous with a blunted weapon than a forceful push because the push provides time for the neck muscles to resist the motion.

That being said, pushing through your target is better technique when using a sword. Swords do not rely on their impact in order to cause damage, rather they do their damage as a result of continuing to cut through a target after the impact. Maximizing impact force, as we might do in boxing, is therefore detrimental because it is more likely to cause the blade to bounce off of the target following the impact and it prevents continued penetration with the blade. This boxing video does a decent job of describing the difference between punching and pushing and the reasons that he gives for why a “snapping” is best for boxing and are the precise reasons why they aren’t good for when you’re using a sword.

Snapping vs. Pushing Punches Video (YouTube)

This test cutting video, while a bit long-winded, provides an example of how this works with a sharp sword. The rest of the video tests out a couple different ways of delivering blows and is worth a watch, but for our purposes, you can skip ahead to the 20:34 mark.

http://www.youtube.com/watch?v=efelZtMbfNk&t=20m34s

Who is Responsible for Controlling These Factors?

If we look at the list of other factors listed above, the key take-away is that the person delivering the blow is largely responsible for causing concussions. While they do not have control over whether their opponent steps into the blow, they are in control over:

1. How hard they strike
2.  The placement of their blows
3. The technique used to deliver their strike
4. Throwing their body-weight into the blow and
5. Their own body movement towards their opponent.

We should therefore consider it the responsibility of the person delivering the blow to control their weapon such that they are not likely to injure their opponent. Importantly, punching and flinging techniques, slipping on the ground resulting in hard hits, failure to control distance, failure to cushion blows, throwing cuts as punches, etc are a form of negligence and as fighters and as marshals, we should be proactive in eliminating these from the field.

Fighters who do these things may be quite capable of delivering blows within the typical force range most of the time, however, these techniques make hard, injurious hits more likely because they remove the fighter’s ability to control their weapon and body. When such blows occur, they are not accidents; they are the result of malice, ignorance, or negligence and should be treated as such.

We should also keep in mind that the recipient of a blow has some control over whether or not they will be injured. The recipient has control over whether they step forward without protecting themselves (i.e. closing the line/parrying, etc) and certainly should avoid footwork that involves flinging themselves forward. Recipients can also control how they receive a blow, but it is not strictly their fault if they receive a hard blow wrong. We should actively train fencers to receive hits correctly and fighters who routinely fail to actively receive blows are a danger to themselves.

The next article will address specific techniques for both the deliverers and recipients of blows to reduce the likelihood of concussions in SCA rapier.

(Ed. This is part of a 5 part series. Comments that indicate a failure to read previous entries shall be mocked and, possible, moderated with extreme prejudice. The author took the time to do the research, you can take the time to read it)

(See Part 1, Part 3, Part 4)

Knowing how much force is required to cause a concussion doesn’t tell us much if we don’t know how hard we are hitting. Fortunately Master Llwyd Aldrydd has created a machine for measuring the force generated by thrusts and has used it to acquire several hundred data points including blows from single-handed rapiers, two-handed swords, and rapier spears. The data he collected is available here for download as an excel document. The analyses presented here were carried out using the data from Pennsic 43 (.xlsx file download) combined with the “second” data collection.

Methods:

A total of 78 fighters delivered a total of 1275 blows using a variety of weapon and blow combinations. Specifically, fighters delivered as many as 3 blows of each of the following types:

1. Single-handed strike with a rapier
2. Single-handed strike with a two-handed sword
3. Two-handed strike with a two-handed sword
4. “Harpooning” strike with a two-handed sword
5. “Fixed hands” strike with an Alchem rapier spear
6. “Pool cue” strike with an Alchem rapier spear
7. “Controlled combat” strike with an Alchem rapier spear

However, not all fighters completed all of the different types of blows. The weapons used varied between individuals. For our purposes here, we will focus on only the single-handed strikes with a rapier. A total of 73 individuals delivered 3 strikes with the rapier, for a total of 219 measured impacts.

Results:

The first step in determining what a “typical” blow is like is to explore measures of centrality. In most cases it is sufficient to look at the mean amount of force, which we can see is about 21 lbs. However, median and mode are other measures of centrality that should be considered when trying to figure out what is “typical.” It is frequently the case in statistics that we assume that data follows a “normal” or “gaussian” distribution, in which case, mean, median, and mode should have the same value. If we look at the data above, we can see that both the median and mode are 20 lbs, which is pretty similar to 21 lbs. I have also chosen to show the descriptive statistics for each of the 3 blows separately because it helps to demonstrate that the “total” is, on its face, representative of the three separate blows.

The next step is to look at how much variance is present in the data. For instance, it is possible that one fighter (or group of fighters) were hitting with 5 lbs while another fighter (or group of fighters) was hitting with 35 lbs of force. Or, alternatively, everybody could be hitting with 20-21 lbs of force. These two situations are very different from each other, and so we need to determine how “wide” our expected window of force should be. A simple method for inferring this is to look at the range. We can see above that blow force ranged from 5 – 40 lbs. This value doesn’t really help us to determine whether 5 lb or 40 lb blow were common nor does it help us to determine whether most fighters were hitting with around 20 lbs of force, so instead we need to use a different measurement such as standard deviation. What standard deviation tells us is how much of a difference from the average to expect. The standard deviation in the sample shown above is around 7.5 lbs, which means that we would expect most blows to land in the range of 13.5 lbs – 28.5 lbs.

The standard deviation is, however, still a rather blunt instrument because it does not take into account the shape of the data. A good way to see the shape of our data is to make a histogram that shows the frequency of each quantity of blow force (Figure left). From this graph, we can see that most of the blows did occur within the 13.5 lb – 28.5 lb range centered around the average, as we might have expected.

As noted above, it is typical to assume that data fits a normal distribution for the purposes of modelling, but that isn’t always true. In fact, if we overlay our “Observed” data with what would be  “Expected” from a normal distribution, we can see that it looks similar (Figure center), but that it doesn’t fit perfectly (Figure 1 middle). Now, we don’t expect that observed data will ever be perfect, so rather than just looking to see if they visually match, we can also do a statistical test called a chi squared goodness of fit test. If we do so, we find that X2(6) = 15.26,p < 0.05, which means it is statistically unlikely that our observed data follows the normal distribution.

I have also generated a third chart (Figure right) that shows how frequently a blow occurs at or below a given force level. From this we can see that 80% of blows fell over the range of 10-30 lbs and that 60% of blows fell in the range of 15-25 lbs, which helps to illustrate precisely how much more frequently blows were to land near the mean than they are at the extremes.

What does this all mean?
For starters, the data demonstrate that typical single-handed blows fall within a range of around 15-30 lbs, which is significantly lower than the force that we calculated to be required to cause a concussion in our previous article. However, we know that concussions do occur as a result of single-handed rapier blows and so we must conclude that 1) fencers hit harder during actual sparring than they do when delivering blows against the machine and/or 2) other factors lead to concussions in SCA fencing.

Additionally, the shape of the distribution of blow force supports the idea that fencers are exerting control over the amount of force that they are delivering. Fencers were more likely to deliver a blow that was similar to the mean and less likely to deliver a blow at the extremes than we would expect if the data followed a normal distribution, which suggests an active selection towards the center, which is encouraging. However, we should keep in mind that some of this tendency towards the middle may be due to the limited range of the sample distribution. It was physically impossible to deliver blows with negative amounts of force, for instance, and so, compared with the normal distribution, the probability of low-force blows is lower in our sample.

This dataset may also provide us with another way of measuring an “excessive” blow. Currently the rules define an “excessive” blow as one that causes injury. This is problematic for a number of reasons, but the obvious one is that it is reactive rather than proactive and waits until after an injury has occurred to set a boundary. It also sets us up for having more injuries. As you can see above, the amount of force delivered by a blow is distributed over a range of forces. If we were to increase the mean while keeping the standard deviation the same, we would expect that the number of hard blows would increase. Similarly, if we were to increase the amount of variability (standard deviation), reflecting reduced control, while keeping the mean the same, we would also expect that the number of hard blows will increase and of course, if we both raised the mean force and increased the variability, we would expect an even greater increase in the number of hard blows. By setting the threshold for an “excessive” blow as one that is injurious, we are creating a situation where the marshalate lacks the tools to curb an increase in mean force and/or the variance.

Rather than defining an “excessive” blow as one that causes injury a better method may be to define an excessive blow as one that is atypically hard. I expect that in practice, this is how calibration is handled by most combatants and marshals. This approach has the benefit of actively driving calibration towards the mean, and this practice may be responsible for the shape of the data seen here (specifically the greater tendency towards the mean than in the normal distribution).

If we were to use this approach, the next step is to figure out how to define a shot that is “atypically hard.” We can handle this in a number of ways, however two simple approaches are as follows: First, we can calculate whether a blow is likely to reflect the sample distribution and  set a threshold value that dictates that the top x% of blows are considered to be excessive. In statistics, a threshold of 5% is frequently used, which would reflect a blow with approximately 38 lbs of force in the current sample. Second, we can treat the problem as a form of outlier detection. In this case, a solution such as the six-sigma method whereby blows that land 6 standard deviations or more above the mean are considered to be excessive. Using the current sample, this would reflect a blow with 66lbs of force. It would be interesting to devise a method to measure the force of a blow and allow a recipient to experience what these levels of force feels like qualitatively. We may be able to do this with a high-speed camera or, alternatively, we could devise a tool that delivers a known amount of force over a cross-section that is similar to our rapier blunts.

Another possible use for this data is in the evaluation of other types of weapons. Llwyd has collected data from two-handed swords and rapier spears delivering a variety of different kinds of blows and it is possible that we could use this data to determine whether these different weapons strike significantly harder than single-handed rapiers. I intend to do this comparison in the near future as part of a separate discussion.

What about cuts?

Sadly, Llwyd’s machine has not (yet?) been used to measure the force of cutting blows. My personal experience with cuts, having now fought C&T in two SCA kingdoms and having some limited experience fighting with HEMA groups outside the SCA is that in general, cuts are delivered with a level of force that is similar to thrusts and that the hardest cuts I have received (ruling out situations where I was actually punched using the guard) are at the very least similar in their level of force to the thrusts that i have received. The society rules for C&T require that blows be delivered with sufficient control so as not to injure opponents and so we might reasonably assume that blow forces will fall within a similar range to thrusts or, at the very least, that cuts will not typically land harder than the hardest thrusts. We could even provide some extra wiggle room and assume that cuts land in a range that is more typical of thrusts by two-handed swords (mean = 26.6 lbs, sd = 9.6, max = 55lbs). In any case, we should not expect that the range of blow forces delivered by controlled cuts should exceed the minimum level of force required to cause a concussion (~100 lbs).

In summary:

The forces measured from thrusts performed using single-handed rapiers are much lower than the threshold we have established for causing a concussion. While no measurements were taken regarding cuts, it is unlikely that cuts typically land five times harder than thrusts, and so we should not expect that either cuts or thrusts will, during typical use, cause concussions on their own. However, the force of the blow may still be a contributing factor in causing concussions, but we must also look towards other factors in order to understand why concussions happen in SCA fencing. These findings should also be considered with the caveat that the human body is certainly capable of delivering the 100 lbs of force necessary and that it remains a possibility that a fighter acting through either gross negligence or through malice can deliver a cut or thrust with sufficient force to cause a concussion.

(See Part 2, Part 3, Part 4)

What is a Concussion?

Until somewhat recently, concussions were seen as a relatively mild injury. However, in the last few years, a growing body of evidence has demonstrated the long-term consequences of these injuries to medical professionals and the public at large. Simply put, a concussion is a form of traumatic brain injury (TBI) caused by impact with the head [1,2,3, 4]. In the short term, symptoms can include disorientation, headache, memory loss, loss of consciousness, an inability to focus, tiredness, lack of coordination, nausea, and dizziness [1,2]. However, high-profile incidents involving former professional athletes combined with a substantial number of veterans returning from Operation Enduring Freedom and/or Operation Iraqi Freedom who have received head injuries has shown that concussions can result in serious long-term consequences including loss of cognitive abilities, depression, aggression, a loss of impulse control, anxiety, post-traumatic stress disorder, and premature death [1,3].

Symptoms of Concussions: 
Concussion Symptoms [Online image]. Retrieved May 5, 2016 from http://www.advancedvisiontherapycenter.com/services/sports_vision/concussion_management/.

Concussions can occur as a result of many different types of activities. For veterans of recent military operations in Iraq and Afghanistan, concussions typically occurred due to explosive devices, gunshot wounds (with and without helmet penetration), and vehicle accidents. Vehicle accidents are also a common cause of concussions [5] for people living their day-to-day lives along with falling and physical assault [1]. Various sports such as football, soccer, hockey, etc can also lead to concussions. In these cases, concussions typically result from impacts with other players or from impacts with the ground [2,3,4]. SCA fencing shares these risk factors for concussions, particularly when we consider participation in melees. Fighters are also at risk for receiving concussions due to sword blows, which is the type of concussions that we will primarily focus on here.

Regardless of the activities that caused the impact, concussions typically occur in one of three ways:

Direct Impact with the Brain: This type of injury involves either the penetration of the skull by a foreign object or an injury that crushes the skull.

Yes, this would also cause a concussion: direct impact with the brain
Spear in Brain [Online Image]. Retrieved May 5, 2016 from http://brainandspine.titololawoffice.com/2012/07/articles/traumatic-brain-injury-tbi/phineas-gage-and-yasser-lopez-offer-modern-brain-injury-research-more-data/.

Linear Acceleration of the head: Acceleration of the head through space can cause the brain to impact the inside of the skull.

Linear acceleration causes the brain to impact the inside of the skull: 
Andrews, M. (2012). Concussion Anatomy [Online image]. Retrieved May 5, 2016 from https://commons.wikimedia.org/wiki/File:Concussion_Anatomy.png.

Rotational Acceleration of the head: Rotation of the head on its axis can create shearing forces inside the brain that cut through neurons causing something called “diffuse axonal damage.” Indeed, rotational injury seems to be most responsible for sports injuries [6].

Concussion due to rotational acceleration leads to shearing of neurons in the brain.
Graves, T. (2014). Concussion [Online image]. Retrieved May 5, 2016 from http://weillcornellbrainandspine.org/condition/concussion.

Given that our blunted weapons should, in no way result in penetration of the skull, we can limit our discussion to concussions caused by either linear or rotational acceleration. The obvious next question is: How much acceleration is necessary to cause a concussion?

Unfortunately determining a clear threshold for injury is tricky. A recent study has shown concussions occurring from football impacts ranging from 60G – 168G (1G = acceleration due to gravity = 9.8 m/s2) [4]. However it is also clear that it is possible to undergo far greater acceleration without sustaining a concussion. For our purposes, it is sufficient for us to use a value on the lower end of this range in order to determine where concussions will start to occur, which gives us a value ~ 60G. However, there is some evidence that lower levels of impact (30G) may be sufficient to cause significant brain damage [5], so keep in mind that this threshold is currently a contentious aspect of concussion literature and is subject to changing due to new research.

How much force is required to accelerate the head 60 Gs?

While calculating the exact level of force is somewhat more complicated, the movement and acceleration of objects can be estimated rather simply using Newton’s First and Second Laws of Motion [7]:

1. An object either remains at rest or continues to move at a constant velocity, unless acted upon by a force. (Inertia)
   
2. The vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration vector a of the object: F = ma.

Linear Acceleration:

In other words, if we want to calculate how much force is needed to cause an object to accelerate a given amount, we will need to know its mass. A human head has a mass of approximately 5 kg and a fencing mask has a mass of approximately 2 kg, so for this calculation, let us assume a mass of 7 kg. First let us convert Gs of acceleration to the more typical metric unit, meters(m)/second(s)²:

A = 60G * 9.8m/s²/G = 588 m/s²

Then in order to calculate the necessary force to cause 588m/s² of linear acceleration, we get:

F = 7kg * 588 m/s² = 4116 kg*m/s²

In the metric system, the unit for force is the Newton (N), which is equal to 1 kg*m/s², so the necessary force to cause this level of linear acceleration is 4116 N. However, I expect that most people reading this series of articles are located in the US and so Newtons aren’t a particularly intuitive unit of measurement. Fortunately the unit for force in the US/Imperial system of measurements is the pound and the conversion factor between these measurements is 4.45 N = 1 lb. We then have:

4116 N = 925 lbs

Rotational Acceleration:

Calculating the necessary force required to cause this level of rotational acceleration is slightly more complicated. Rotational force is calculated using a slightly different equation, so rather than using F = M * A, we instead calculate for torque:

torque(τ) =moment of inertia( I) * angular acceleration(α)

Since we have already converted from Gs to m/s2, we must now calculate the moment of Inertia. The equation for this is as follows:

I = constant (k) * mass (m) * radius (r)²

Location of the atlas (shown in red) and axis (immediately below and encapsulated by the atlas). These bones form the joints that allow the head to rotate.
Anatomography. (2012). Atlas [Online image]. Retrieved May 5, 2016 from https://commons.wikimedia.org/wiki/File:C1_lateral.png.

So now, in addition to knowing the mass of the head, we must also know its radius. Anatomically the head rotates vertically (nodding) in the joint between the occipital bone of the skull and the atlas bone and horizontally (side-to-side) in the joint between the atlas bone and the axis bone (the atlas is shown in red above and the axis is mostly obstructed by the atlas, but is visible as a small sliver of white under the atlas). Knowing this, we can measure from this point to the chin of a fencing mask, which is around 10 cm. We can therefore calculate I as follows:

I = k * 7kg * 0.1 m² = k * 7 * 0.01 m = k * 0.07 kg*m²

You will note that this leaves the term, k which I have not yet defined. In this equation, k is a constant term that is dependent on the shape of the object being rotated. Choosing an appropriate k-value is complicated, so let us come back to it. For now, let k = 1. We can then finish calculating the necessary force to cause this kind of rotational acceleration:

τ = 0.07 kgm²*588m/s² = 41.16 N*m

In this case, the “meters” part of the result is related to the radius, so we can get rid of it as follows:

41.16 N*m / 0.1 m (the radius) = 411.6 N = 92.5 lbs

Choosing a value for k

Calculating a precise value for k is tricky because the head, particularly a head encased in a fencing mask is strangely shaped, the axis of rotation is off-center, and the mass is not uniformly distributed, however we can estimate a value for k by selecting a geometric shape that is similar to the shape of the head and using its k value here. That is, As the old physics joke goes, assume a spherical head. In this case, the value for k is 0.4. So, taking that into consideration, we would then multiply our result by this value:

411.6 N * 0.4 = 164.64 N = 37 lbs

Given that we’re “fudging” the shape of the head here, we should take this value with a grain of salt and understand that the correct value should lie somewhere between these two values. In other words, the needed force is somewhere between 164.64 N – 411.6 N or in Imperial measure, 37 lbs – 93 lbs. 

Editing Note: These calculations will be addressed again in article 5 to use experimentally-derived values for moment of inertia.

Conclusion:

From the perspective of our combat sport, rotational acceleration poses the greatest risk for concussions, which is consistent with research into concussions in other sports. Importantly, the level of force needed to cause a concussion due to rotation is relatively low. In the next article, we will compare these levels to the measurements of striking force carried out by Baron Llwyd.  

Works Cited:

1. Centers for Disease Control and Prevention. (2015). Report to Congress on Traumatic Brain Injury in the United States: Epidemiology and Rehabilitation. National Center for Injury Prevention and Control; Division of Unintentional Injury Prevention. Atlanta, GA. http://www.cdc.gov/traumaticbraininjury/pdf/tbi_report_to_congress_epi_and_rehab-a.pdf
2. McCrea M, Guskiewicz KM, Marshall SW, et al. Acute Effects and Recovery Time Following Concussion in Collegiate Football Players: The NCAA Concussion Study.JAMA. 2003;290(19):2556-2563. doi:10.1001/jama.290.19.2556.
3. Guskiewicz KM, McCrea M, Marshall SW, et al. Cumulative Effects Associated With Recurrent Concussion in Collegiate Football Players: The NCAA Concussion Study.JAMA. 2003;290(19):2549-2555. doi:10.1001/jama.290.19.2549.
4. Guskiewicz KM, Mihalik JP, Shankar V, et al. (2007). “Measurement of head impacts in collegiate football players: Relationship between head impact biomechanics and acute clinical outcome after concussion”. Neurosurgery 61 (6): 1244–52; discussion 1252–3.doi:10.1227/01.neu.0000306103.68635.1a.
5. Varney NR, Roberts RJ. Forces and accelerations in car accidents and resultant brain injuries. In: Varney RN, Roberts RJ, editors. The Evaluation and Treatment of Mild Traumatic Brain Injury. Mahwah, NJ: L Erlbaum; 1999. pp. 39–47.
6. R.C. Cantu. Guidelines for return to contact sport after a cerebral concussion. Phys Sports Med, 14 (1986), pp. 75–83
7. Barth, J. T., Freeman, J. R., Broshek, D. K., & Varney, R. N. (2001). Acceleration-Deceleration Sport-Related Concussion: The Gravity of It All. Journal of Athletic Training, 36(3), 253–256.