Wireless Sensor System for Rugby Impact Assessment
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Published: Wed, 30 Aug 2017
Throughout the years, the rate and severity of injuries in sports have drastically increased. Athletes tend to become bigger, faster and stronger. In contact sports such as rugby, boxing, American football, etc., athletes and enthusiasts risk their health and well-being exposing their bodies to the stress and injuries present in sports. This thesis is more focused on head injuries, concussions to be specific. Concussions or any brain damage tend to affect the athletes mostly later on in life, causing dementia, permanent headaches, dizziness, difficulty concentrating or completing tasks, irritability, anxiety, memory loss, the list goes on.
Anyone that has ever played a sport and had an injury, is now more aware than before of the risks of playing whatever sport the person was playing when the injury occurred. Not that being aware is going to prevent injuries, but at least the practitioner won’t be surprised when something unexpected happens or at least the practitioner will be in a position where he can decide if is really worth the risk.
As a sports enthusiast I have always been interested in sport, and I have always practiced sports. Summer of 2012 I started playing American football, I loved the rush of the game and the fact that I was so fast that they couldn’t catch me. As months went by, the whole team was getting ready for the beginning of the season, everyone was becoming bigger, faster, and stronger, and therefore the impacts during collisions and tackles were becoming more taxable on the body. It was part of the routine to do an exercise we used to call “Bull fight”, where we knock heads against each other so we can get used to the impact. The first time I did this I felt dizzy, but as a teenager I didn’t think much about it. First game of the season, I was getting ready to score my first ever touchdown, I got tackled. I was unconscious on the floor for two minutes, they said. I was taken to the local doctor for a quick check up to make sure everything was ok with me. The doctor said that I most definitely have had concussion. After I have done some research into the topic, I kind of realised the risk I was exposing myself too, every time I carried an American football. When we talk about American football, every contact sport serves as example and in this dissertation we will focus more on rugby.
My main motivation to do this project is the fact that I believe that a major part of the population that practices sports, specifically contact sports, don’t know the consequences on the long run of doing so. I hope that with the realisation of this project I can create an impact towards sports enthusiasts like myself, not in a way to make them give up on the sport, but at least they will be aware of their actions, and maybe adopt the use of safer gear when playing the sport, as most players don’t use the equipment available like the rugby helmet.
And my question are: Do athletes or enthusiasts really know what type of circumstances and risks they are exposing themselves to? And can this injuries be prevented or can the risk exposure be reduced?
The dissertation will focus on the design and testing of a neck portable system capable and efficient at monitoring the linear and angular head acceleration, which has been described as a very efficient way of assessing the force impact that players go through during practice or a serious game, as shall be demonstrated during this thesis.
The main aims of this project is to conduct background research on rugby injuries statistics, accelerometers and portable sensors, to find the best design for this project, implement and test it using an Arduino chip, to calibrate the system against involuntary accelerations, to investigate the portability, usability and applicability in rugby and other contact sports, and to demonstrate the collected results and visualisation.
In order to conclude this project successfully a general insight will be acquired through background research. Therefore the section 2.1 will represent an in depth research about injuries in rugby, a comparison between youngsters, seniors and professional players, section 2.2 will explain the concepts related to accelerometers, different types of accelerometers, price ranges, advantages and disadvantages of each, section 3 will focus onÂ the importance of measuring the linear and angular head acceleration, section 4 will explain the two different types of interface, SPI and I2C, and detail the I2C interface as is the interface that is going to be used during this project, section 5 will demonstrate the design and implementation of the project by displaying pictures of the first prototype, and final project, the reason why such design was chosen and all the steps followed, finally the section 6 will demonstrate all the testing done in different scenarios, and respective results of the prototype and the final project, all represented using, graphs and tables . Since the project is also an investigation on how efficient the project is going to be during a game or practice, some ideas and small tests will be carried out in the end.
An equipment of this category, will be really useful in any contact sport, as it will provide important information to monitor the force exerted towards a head, and carry on further studies in the area of concussions and other brain damages that frequently occur in rugby players, or other athletes performing contact sports. It can also increase the attention towards adopting safer protective gear.
Head injuries are really frequent in contact sports such as rugby, occurring more in situations like the scrum, head impacts on the floor, etc. The most common head injury is called concussion, however that’s the most minor kind of head injury (Lava). A concussion occurs at 90 to 100 g-force, equivalent to a head impact of 20mph (Gorgens, 1). 65% of head injuries occurred in rugby are laceration, 17% concussions and 9% are fractures to the skull (Kaplan et al. 91). Due to the high chance of head injury, the RFU (Rugby Football Union) has found ways to prevent these unfortunate situations. Some of them being laws, regulations, guideline based on research evidence, concussion awareness, first aider and health care and professional player testing courses.
“Rugby Union is on a pinnacle of success and popularity” (Edgar, 1995), this attracts the media, the media attracts the population, therefore the interest for the sport, practitioners, researches and experiments increase exponentially as well, placing more emphasis on finding ways to protect our athletes.
A study carried out by UU at schools in Northern Ireland discovered a “high rate of severe injury” in rugby to rugby players in schools (Meredith, 2016). A total of 825 students from 28 different school teams participated in the study during 2014/2015, which resulted in 426 injuries, 204 of them resulting in an incapability of practicing the sport for an average of four weeks. One in four rugby players will suffer an injury, 55% of the injuries occur during a tackle, 78% of concussions specifically occur during a tackle, 13% are knee injuries, 7% hand injuries, 10% concussions, 11% ankle injuries, 10% shoulder ligament injuries and 5% shoulder dislocation. After calculating it reveals that it occurs three concussions per team. “Young athletes are more vulnerable to concussion and may be affected by more complicated recovery times and higher risk of adverse outcomes.” (Meredith, 2016). On 29 Of January of 2011 a drastically accident happened to a young player, 14 years old named Ben Robinson while playing rugby union for his school team. During the game he had three impacts to the head, on each impact he was taken off the field and put back, on the fourth impact he collapsed and died later on in the hospital (Bull, 2013).
As cases like the death of Ben Robinson happen once in a while it will automatically increase the urgent increase for awareness, researches and solutions to this problem. “Enforcing the laws of the game is definitely one, that’s things like looking at the height of the tackle, ensuring that it’s interpreted properly, and teaching good tackling technique,” (Bleakley, 2015). Some rules that could be applied would be in case of a brain injury like concussion the player shouldn’t play for at least 30 days, like applied in boxing, the player shouldn’t have to play under effect of pharmaceuticals to don’t feel the damage caused by the injury suffered, among other rules.
Rugby is the sport with highest risk of injury. It was stated that “Paradoxically at the international level, where the game is fastest and most spectacular, evidence shows that fitness and experience considerably reduce the injury rate.” (Addley and Farren, 1988), however a research carried out in English premiership academy and schools rugby union, concluded that the rate of injuries in academy and school youth rugby union and fairly lower than the rate of risks recorded for senior elite rugby union (Palmer-Green, Trewartha and Stokes, 2009). Personally I don’t agree with the first statement, as the higher the level of the game, the higher the physical characteristics of the players and the faster the pace of the game, which increases the strength of collision involved.
As the years go by, the rugby rules have been changing trying to create a safer way to play the game, however is still not good enough, It still a really high chance of injury by playing the sport. Is understandable if someone adult knows the risk of playing the game, accepts it and takes responsibility upon any consequences, but maybe anyone under 18 that is not capable of making the best decisions shouldn’t play such an aggressive game or at least with not as much contact as they do.
An accelerometer senses positive and negative accelerations of a body. It works by sensing the acceleration of gravity and allows us as well based on the results produced, to calculate the direction of the acceleration. It uses the technology MEMS, that stands for Microelectromechanical systems, however that’s the term used in the United States of America, In United Kingdom the term used is MST, that stands for microsystems technology (Maluf and Williams, 2004). MEMS are similar to an integrated circuit but they are mechanical. The technique used to make MEMS are the same as the technique used to make electronics, microfabrication, but instead it’s made small mechanical structures that can interface with electronics (Afrotechmods, 2014).
Acceleration is the rate at which the velocity of a body changes with time (Nisticò, 2013).
Accelerometers can be used for different applications. They can be used for automotive applications such as airbags control, motion sensing, GPS, navigation. They can be used in seismometers, camera stabilization, to play games, smartphones, etc.
An accelerometer has six sensing functions:
Movement – covers motion control and general movement detection
Fall identifies that a large impact is highly likely to happen. Can be used for motion control
Tilt – can be applied to mobile phones to detect whether is facing up or down, text scrolling, lcd projection, user interfacing, image rotating, camera stability, etc.
Positioning – requires more complex algorithms than the others. It can be used in a GPS and personal navigation
Shock – Can be used in situations of shipping and handling, car event data recorders and hard disk drive protection
Vibration – Mostly used in cases where high sensitivity and high frequency accelerometers are needed. Such as seismic activity monitors and acoustics
For every situation there will be the best choice of accelerometer, as every range of acceleration has different applications. For example fault detection and tilt control is in the range of 1G to 2G, shock detection lands on the 2G to 8G range, vibration 8G to 10G range, an odometer 20G to 30G range, a car crash can range from 20G to 250G and a bullet can go up to 5000G (G. Ogden, 1895).
When measuring free fall the values can be positive or negative, and for best results it requires a height of at least one meter. There is three types of freefall, linear, rotational and projectile. A linear freefall, is when there is a drop from certain height straight to the, a rotational freefall is the same as the linear freefall, however a spin or rotation is added to the travel of the body, the projectile freefall is when the body is thrown away, and it includes horizontal movement as well as a vertical movement and it will also have a small rotation (FarnellElectronics, 2011).
When measuring the tilt, there is some things to take in consideration. The accelerometer needs to be mounted in a way so the axis of sensitivity is parallel to the surface used. The formula used to calculate the output is the follow: Vout = sensitivity of the accelerometer multiplied by 1G times the tilt of the angle plus the offset voltage of the accelerometer. The output can vary from -1G to 1G, and detects angles from -90 to 90 degrees (FarnellElectronics, 2011).
There is some considerations needed to be taken when measuring the position. First is the displacement, how far the accelerometer will be moving to detect the change in movement. The range of the device is really important. If it’s going to be tested on a person, is going to be produced a higher G force and requires an accelerometer that supports a higher G force range, If it’s going to be a very small change such as a mouse it requires an accelerometer with a really high sensitivity (CH Robotics, 2017).
When measuring shock the biggest thing to consider is the G-range. The accelerometers uses the deceleration of the object to determine the shock, like tapping or a car crash. To measure the vibration, the closer the accelerometer is from the vibration source, the higher the G value (Morrow, 1974). For measure vibration the most important thig is the frequency of the vibration, the second thing to consider is the G range, similar to previous situations, for every application there will be a different type of accelerometer, and where the accelerometer is mounted will affect the readings as well.
Below is represented on how the g force is spread through the axis:
Between a DC- response accelerometer and an AC-response accelerometers, DC is the most recommended one as AC-response accelerometers can’t measure static accelerations, slow vibrations or sustained accelerations due to being AC coupled.
The main types of accelerometers are the ones listed below.
Capacitive – DC coupled. Produces an output based on capacitance changes. They are smaller and cheaper than the average accelerometer (Mineta et al. 431-435). They are mostly found in phones, gaming platforms (Wii, Xbox, etc)
Piezo resistive – DC coupled. Produces an output based on the resistance changes, under strain gauges that are part of the accelerometers seismic mass. Commonly used in shock events due to its high frequency range, amplitude and wide bandwidth (Partridge et al. 58-62). They are very accurate, as they can measure as low as 0 Hz, but they are not a good choice to test low frequency vibrations due to lack of sensitivity (Voldamn 2007).
Piezoelectric – AC coupled. Produces an output based on an electric charge proportional to the force suffered under acceleration. Mostly used for test and measurement roles, due to its high frequency, sensitivity and simplicity (Tian et al. 2). However because they are not DC coupled, is a bad choice in situations with high displacement or velocity as it can’t detect low vibrations, or high acceleration levels.
Below is listed in a resumed way the characteristics of each accelerometer.
Low frequency vibration
High frequency vibration
High impact shock
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