A Review of Instrumented Equipment to Investigate Head Impacts in Sport

Contact, collision, and combat sports have more head impacts as compared to noncontact sports; therefore, such sports are uniquely suited to the investigation of head impact biomechanics. Recent advances in technology have enabled the development of instrumented equipment, which can estimate the head impact kinematics of human subjects in vivo. Literature pertaining to head impact measurement devices was reviewed and usage, in terms of validation and field studies, of such devices was discussed. Over the past decade, instrumented equipment has recorded millions of impacts in the laboratory, on the field, in the ring, and on the ice. Instrumented equipment is not without limitations; however, in vivo head impact data is crucial to investigate head injury mechanisms and further the understanding of concussion

Analysis of head acceleration events in collegiate-level American football: A combination of qualitative video analysis and in-vivo head kinematic measurement

The contact nature of American football has made head acceleration exposure a concern. We aimed to quantify the head kinematics associated with direct helmet contact and inertial head loading events in collegiate-level American football. A cohort of collegiate-level players were equipped with instrumented mouthguards synchronised with time-stamped multiple camera-view video footage of matches and practice. Video-verified contact events were identified as direct helmet contact or inertial head loading events and categorised as blocking, blocked, tackling, tackled or ground contact. Linear mixed-effects models were utilised to compare peak head kinematics between contact event categories. The timestamp-based cross-verification of the video analysis and instrumented mouthguard approach resulted in 200 and 328 direct helmet contact and inertial head loading cases, respectively. Median linear acceleration, angular acceleration and angular velocity for inertial head loading cases was greater than direct helmet contact events by 8% (p = 0.007), 55% (p 0.05). The study highlights the potential of combining qualitative video analysis with in-vivo head kinematics measurements. The findings suggest that a number of direct helmet contact events sustained in American football are of lower magnitude to what is sustained during regular play (i.e. from inertial head loading). Additionally, the findings illustrate the importance of including all contact events, including direct helmet contact and inertial head loading cases, when assessing head acceleration exposure and player load during a season of American football

Low-rank representation of head impact kinematics: A data-driven emulator

Head motion induced by impacts has been deemed as one of the most important measures in brain injury prediction, given that the majority of brain injury metrics use head kinematics as input. Recently, researchers have focused on using fast approaches, such as machine learning, to approximate brain deformation in real-time for early brain injury diagnosis. However, those requires large number of kinematic measurements, and therefore data augmentation is required given the limited on-field measured data available. In this study we present a principal component analysis-based method that emulates an empirical low-rank substitution for head impact kinematics, while requiring low computational cost. In characterizing our existing data set of 537 head impacts, consisting of 6 degrees of freedom measurements, we found that only a few modes, e.g. 15 in the case of angular velocity, is sufficient for accurate reconstruction of the entire data set. Furthermore, these modes are predominantly low frequency since over 70% to 90% of the angular velocity response can be captured by modes that have frequencies under 40Hz. We compared our proposed method against existing impact parametrization methods and showed significantly better performance in injury prediction using a range of kinematic-based metrics -- such as head injury criterion and rotational injury criterion (RIC) -- and brain tissue deformation-metrics -- such as brain angle metric, maximum principal strain (MPS) and axonal fiber strains (FS). In all cases, our approach reproduced injury metrics similar to the ground truth measurements with no significant difference, whereas the existing methods obtained significantly different (p<0.01) values as well as poor injury classification sensitivity and specificity. This emulator will enable us to provide the necessary data augmentation to build a head impact kinematic data set of any size.Comment: 20 pages, 13 figures, 4 table

An assessment of one-on-one inertial shoulder tackles in rugby league using instrumented mouthguards and qualitative video analysis.

In the recent past, head injuries in rugby union and league have been a cause for concern. Making use of instrumented mouthguards enables the recording of head acceleration events (HAE) experienced by athletes in real time. Increased magnitude and frequency of HAEs increases the risk of head injuries such as concussion. The aim of the study was to examine the effect different tackle types have on peak linear acceleration (PLA), peak angular acceleration (PAA) and peak angular velocity (PAV) during one-on-one inertial shoulder tackle HAE. The study involved the analysis of 80 tackles on male Leeds Rhinos players collected over 27 Super League matches. PLA, PAA and PAV of the head were recorded using the instrumented mouthguards with a 5 g or 500 rad/s2 triggering threshold, which is lower than the recommended threshold of 10 g. Qualitative video analysis was done to classify the tackles based on tackle height, tackler and ball carrier speed, tackler and ball carrier body position, tackle direction and whether the tackle was active or passive. Multiple linear regression was done to assess whether the different tackle types influenced PLA, PAA or PAV. Tackler speed and tackle height were determined to be significant predictors of PAV (p < 0.05). An increase in tackle height (B= 2.1, p < 0.05) and tackler speed (B= 1.08, p< 0.05) led to increased PAV. None of the other independent variables significantly predicted PLA, PAA or PAV. Majority of the impacts were below the recommended triggering threshold of 10 g. In conclusion, this study found that an increase in tackler speed and tackle height led to an increase in PAV. In addition to this, the study highlights the efficacy of using a combination of qualitative video analysis and instrumented mouthguards to quantify and categorise HAE in rugby league

Biomechanics of Head Impacts in an Unhelmeted Sport

Concussion in sport is very common and often the injury is undetectable using CT and MRI scans. In addition, approximately 50% of concussions areunreported.The project initially investigated the suitability of a skin patch sensor and a head-band sensorfor the measurement of head impacts in unhelmeted sports. It was found that both were unsuitable due to large angular accelerationerrors. Thestudy then collaborated withCAMLab at Stanford University and 25 Mixed Martial Arts (MMA) athletes were fitted CAMLab’s validated instrumented mouthguard. 451 video confirmed impacts were recorded at 19 sparring and 11 competitive MMA events. Five concussions were diagnosed during the competitive events. The most severe impacts were simulated using the Global Human Body Model Consortium head model. The average resultant linear acceleration of the impacts that resulted in a concussion was approximately 20% lower than concussive studies of US football while the resultant average angular acceleration was 34% higher. It ishypothesised that these differences are due to the high energy frontal impacts in US football as opposed to the ‘hook’ style punches in MMA.Large strains in the mid-brain occurred from frontal impacts whereas lateralimpacts resultedin large strains in the corpus callosum. It was found that the average strain in the corpus callosum of the concussed athletes was 0.27 which was 88% higher than that in uninjured fighters. In collaboration with the Genetics department in Trinity College Dublin it was found that the maximum principal strain correlated (R2=0.84) with the volume fraction of blood brain barrierdisruptionpost-fight. In conjunction with Stanford University,it was found that the spectral density of MMA impacts was higher than that in US football.This study is the first known study to measure in vivohead impacts in unhelmeted athletes that have suffered a concussion

The use of P3b as an indicator of neurophysiologic change from subconcussive impacts in football players

There is a growing appreciation in research that subconcussive impacts may affect cognitive functioning. Canadian University football players (n=45) were separated into three groups based on their position/skill (small skilled, big skilled and big unskilled). An impact measuring device (GForceTracker) was used to record the number of impacts that each player experienced in a season. Player groups were separated into two levels of impact exposure: low and high. Players completed baseline, midseason, postseason, and follow-up neurophysiological tests (four months later) to measure P3b amplitude in response to a visual oddball paradigm, and high versus low impact subgroups for each player group were compared. Small skilled and big skilled players showed significant decreases in P3b amplitudes at midseason and postseason, reflecting decreased attentional resources allocated to the task. No skill group exhibited a significant change from baseline at follow-up, illustrating that in-season cognitive function deficits appear to recover in the offseason

The Performance of Helmet-Based Kinematic Measurement Systems: Importance for Mild Traumatic Brain Injury Prevention

It is estimated that millions of mild traumatic brain injuries (mTBIs) occur each year, and studies show that these injuries can have more long-term neurological consequences than previously thought. High impact sports provide a unique real-world opportunity to study the biomechanical inputs that lead to mTBI and helmet-based instrumentation can be used to estimate the kinematics of head impacts in sports. In Chapter 1, we evaluate two helmet-based measurement systems that use different approaches to estimate kinematics by impacting a helmeted anthropometric test device (ATD) in a laboratory setting. The relationships between the helmet sensor system and reference ATD measures are evaluated. In Chapter 3, we explore the effect of real-world impact and usage variations on the relationships between helmet system and ATD-measured head impact kinematics. The factors varied include the interface between the head and the helmet, repeatability of sensor/helmet systems, helmet geometry/construction, effective mass of the torso, and impacting surface. In Chapter 4 we assess the effect of helmet-based sensor performance on brain injury metrics calculated using finite element analysis. This is done by using helmet system and ATD data from the laboratory impacts as inputs into a finite element head model and comparing outcomes. Chapter 5 discusses the implications of the findings on the implementation of helmet-based systems in real-world scenarios

Evaluating footwear “in the wild”: Examining wrap and lace trail shoe closures during trail running

Trail running participation has grown over the last two decades. As a result, there have been an increasing number of studies examining the sport. Despite these increases, there is a lack of understanding regarding the effects of footwear on trail running biomechanics in ecologically valid conditions. The purpose of our study was to evaluate how a Wrap vs. Lace closure (on the same shoe) impacts running biomechanics on a trail. Thirty subjects ran a trail loop in each shoe while wearing a global positioning system (GPS) watch, heart rate monitor, inertial measurement units (IMUs), and plantar pressure insoles. The Wrap closure reduced peak foot eversion velocity (measured via IMU), which has been associated with fit. The Wrap closure also increased heel contact area, which is also associated with fit. This increase may be associated with the subjective preference for the Wrap. Lastly, runners had a small but significant increase in running speed in the Wrap shoe with no differences in heart rate nor subjective exertion. In total, the Wrap closure fit better than the Lace closure on a variety of terrain. This study demonstrates the feasibility of detecting meaningful biomechanical differences between footwear features in the wild using statistical tools and study design. Evaluating footwear in ecologically valid environments often creates additional variance in the data. This variance should not be treated as noise; instead, it is critical to capture this additional variance and challenges of ecologically valid terrain if we hope to use biomechanics to impact the development of new products