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The week in Biomechanics #CW24

Lasse Hansen 0

Last updated on June 22, 2020

The weekly recap of what is going on in the world of biomechanics.

Last Saturday, a technical note was published in Sports Engineering that caught our attention. A group of researchers tested the reliability of an instrumented mouthguard, aiming to measure impacts to the head during games of rugby union. We will talk quite a bit about the history of head impact measurements before the study is presented. Also, Jonas writes about the experience he gained during the last two weeks at the Special Topics in Sports Engineering 2020. So grab a coffee and enjoy the read!

  1. Comparison of head impact measurements via an instrumented mouthguard and an anthropometric testing device
  2. Special Topics in Sports Engineering 2020

Comparison of head impact measurements via an instrumented mouthguard and an anthropometric testing device

The long-term effects of (micro)concussions and repeated impacts to the head during contact sports are arousing more and more attention due to dramatic and tragic individual cases. But problems do not only occur in the long run, as in rugby union, american football, ice hockey, and boxing injuries following a collision account for 12-33% of all time-loss injuries.

In scientific literature, the head impact exposure (HIE) is used do describe the number of head accelerations above a normal threshold experienced by one individual participating in contact sports. While this factor is extremely handy to compare risk exposure in different contact sports, a standardized way to measure and calculate the HIE is needed and a bunch of studies already discussed several ways (have a look at the paper’s references if you want to read more about this). To measure the acceleration, you might either use a marker-based video analysis or inertial sensors. The severity of the impacts is described by multiple metrics, as for example the head injury criterion (HIC). This method integrates the acceleration signal over a given time span (e.g. 15ms) around the peak linear acceleration. Other procedures combine linear acceleration, rotational acceleration, HIC, and other variables to a single score, which has shown to be the best way to predict a concussion (it’s called Head Impact Telemetry Severity Profile, or HITSP).

Traditionally, studies of this type focussed on helmeted sports. Accelerometers and necessary electronics could be located in the helmet, using multiple accelerometers also rotational acceleration could be measured. More recently, non-helmeted contact sports got into the focus of science. While skin mounted sensors were used and validation studies were run, they have shown to have problems in estimating the movement of the skin relative to the underlying bone. In low-impact speeds this was alright, but with higher speeds it got quite imprecise.

So multiple groups of researchers started to work with instrumented mouthguards, in 2010 a study using a single dual-axis accelerometer was conducted Later three accelerometers were used, and eventually, triaxial accelerometers plus gyroscope inertial sensors came to use. This allowed the acquisition of more thorough datasets, and multiple studies were run with athletes in american football, boxing, and MMA. The absolute advantage of instrumented mouthguards over skin-based sensors is the chance to use these in competitive sports, and not just for field testing since these mouthguards agree with regulations that prohibit clothing or skin-based sensors. It might be possible to quantify HIE of an individual player per game, season, or even career and adjust regulations in favor of the athlete’s welfare.

So let’s talk about what the researchers did, besides investigating the insightful history of HIE research. A pendulum-based impacter was constructed, with a cylindric weight (8.69kg) impacting an instrumented dummy. Actually, the group used a laboratory that usually investigates vehicle safety.

Image Credit:Greybe et al.

After conducting multiple impacts the group found no significant differences between test and retest, therefore concluding to have a reliable measurement. Comparing between different measurement systems, the instrumented mouthguard also appeared to show valid results. If you are interested in the exact setup, sensor specifications, and details of the methods give the article a read, as it’s fully open source.

If you are happy with the details we showed you here, let us conclude with the statement that this method seems to work pretty well and makes a lot of different field studies possible. To us, especially the possibility to track long term exposure during training and competitive play and maybe adapt regulations appears extremely promising.

We are excited to see which ideas other groups come up with having this tool!

Greybe, D.G., Jones, C.M., Brown, M.R. et al. Comparison of head impact measurements via an instrumented mouthguard and an anthropometric testing device. Sports Eng. 23, 12 (2020).

Special Topics in Sports Engineering 2020

A recap by Jonas Ebbecke

This year I was in the fortunate position of being able to participate in the two-week “Special Topics in Sports Engineering” program. This is an annual intensive program of the TU Delft, in which every interested Master student with a background in academia such as biomechanics, (sports) engineering, sports science, or similar can participate. International students (like me from Germany) are also welcomed to participate. The overall goal of this course is to be able to come up with a mathematical model after these two weeks, which can predict the finish time of a cyclist on a certain course. Unfortunately, this program (like basically every event this year) was held online for the first time without attendance at all.

The basics for the aspired model were laid in several lectures. These were held by experts from various institutions in the Netherlands, Great Britain, Denmark, and Germany. Topics like modeling in cycling, cycling dynamics, musculoskeletal modeling, aerodynamics, thermophysiology, performance in endurance sports, material doping, cycling biomechanics, and bicycle design were discussed intensively. All contents were well-coordinated, and the program was clearly focused. We aimed to learn how humans interact with sports equipment and how to quantify performance in cycling. And that’s what we did, as the lectures were not only highly interesting but also designed that complex content was presented in a way everyone was able to understand.

What was learned in the lectures was consolidated by a total of 3 assignments that had to be completed during the intensive program. Therefore, we were divided into small groups of 4 students. My group consisted of Jeroen van der Knaap and Wessel van Veenen from the Netherlands as well as Leonard Arnold and me from Germany. None of us knew each other before, but the group was a good fit and so it was a lot of fun to find the best solution for each task together.

The first task was to determine the resistive forces acting on an athlete and his bike when cycling and in the second we had to determine the physiological capacity of this athlete. Jeroen volunteered as the test person, because his racing bike was equipped with the right measuring technology, so that he could carry out all necessary experiments (and yes – he really suffered from time to time). The third task was to combine all our newly acquired knowledge and the results of the first two assignments and to develop a mathematical model that predicted the target time of the 400 m time trial. This worked surprisingly well for our group. If you are interested in the results, you can read our final report here.

But the pure knowledge and its application in practice was only a part of what we learned in the two weeks. For me, it was even more interesting to meet new people from other fields and experience their way of thinking. The whole field of sports science, -biomechanics and -engineering is huge and multifaceted, yet the transitions between them are fluid and in the end, everything takes place under the same roof. Here it is especially important to network with people from every related discipline and at least to understand what they are basically thinking and doing. This would probably have worked even better if we had all completed the program together in Delft, but that should not diminish the benefit we all gained.

Many thanks at this point to my team and to the organizers for the great time!

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