The role of player mass and contact speed on head kinematics and neck dynamics in rugby union tackling.

Tackling is the most common cause of general injuries in rugby union, with player speed and mass identified as risk factors. This study aimed to use multibody modeling simulations to examine how tackler and ball carrier mass and contact speed affect inertial head kinematics and neck dynamics. Simulations were run by independently varying the ball carrier and tackler mass (from 60 to 110kg) and speed (from 0 to 10 m/s). Peak resultant inertial neck dynamics (force and moment) and head kinematics (linear acceleration, angular acceleration, and angular velocity) were extracted from each simulation. The greatest inertial head kinematics and neck dynamics sustained by a player was when there was the greatest mass disparity in the tackle, with the lighter player experiencing greatest inertial neck dynamics and head kinematics by up to 24% in comparison with the scenario when both players were the lightest mass (60 kg). As a player's mass increased, the magnitude of their head kinematics and neck dynamics diminished, but increased for their direct opponent, irrespective of whether they were the tackler or ball carrier. For speed, the greatest inertial head kinematics and neck dynamics sustained by the ball carrier and tackler were when they were both traveling at the highest speed. In theory, large discrepancies in mass of players, and high speeds into a tackle should be avoided.

Assessment of deep learning pose estimates for sports collision tracking.

Injury assessment during sporting collisions requires estimation of the associated kinematics. While marker-based solutions are widely accepted as providing accurate and reliable measurements, setup times are lengthy and it is not always possible to outfit athletes with restrictive equipment in sporting situations. A new generation of markerless motion capture based on deep learning techniques holds promise for enabling measurement of movement in the wild. The aim of this work is to evaluate the performance of a popular deep learning model "out of the box" for human pose estimation, on a dataset of ten staged rugby tackle movements performed in a marker-based motion capture laboratory with a system of three high-speed video cameras. An analysis of the discrepancy between joint positions estimated by the marker-based and markerless systems shows that the deep learning approach performs acceptably well in most instances, although high errors exist during challenging intervals of heavy occlusion and self-occlusion. In total, 75.6% of joint position estimates are found to have a mean absolute error (MAE) of less than or equal to 25 mm, 17.8% with MAE between 25 and 50 mm and 6.7% with MAE greater than 50 mm. The mean per joint position error is 47 mm.

The incidence and mechanism of heading in European professional football players over three seasons.

There are concerns surrounding the risk of neurodegenerative diseases associated with football (soccer) heading. The aim of this study was to conduct analysis on the incidence and mechanism of heading in the "Big 5" professional European football leagues (Bundesliga, Ligue 1, Premier League, La Liga and Serie A) and one lower tier professional league (English Championship) from 2016/17 to 2018/19. Match event data from 7147 matches were obtained from Opta Sports data feed. The data were parsed to extract header event details including player position, coordinates on the field, header type and preceding match event (including distance football travelled). Incidence data were reported as headers per match or match headers per player. Medians and interquartile ranges (IQR) were reported and either the Mann-Whitney U test or Kruskal-Wallis test were conducted for comparisons between positions and leagues. In the "Big 5" leagues, the most headers per match occurred during the Premier League (111.2 headers per match). However, the lower tier English Championship had the highest number of headers per match overall (139.0 headers per match). In all leagues, defenders had the greatest median number of match headers per player (P < .001). The highest median distance travelled by the football during a preceding match event was for goal kicks (57.5 m; IQR 53.7-61.1). The findings add necessary information for current longitudinal studies aiming to understand the potential link between football heading and neurodegenerative diseases. These studies should account for league, playing position, and level of play.

Force experienced by the head during heading is influenced more by speed than the mechanical properties of the football.

There are growing concerns about the risk of neurodegenerative diseases associated with heading in football. It is essential to understand the biomechanics of football heading to guide player protection strategies to reduce the severity of the impact. The aim of this study was to assess the effect of football speed, mass, and stiffness on the forces experienced during football heading using mathematical and human body computational model simulations. Previous research indicates that a football header can be modeled as a lumped mass mathematical model with elastic contact. Football headers were then reconstructed using a human body modeling approach. Simulations were run by independently varying the football mass, speed, and stiffness. Peak contact force experienced by the head was extracted from each simulation. The mathematical and human body computational model simulations indicate that the force experienced by the head was directly proportional to the speed of the ball and directly proportional to the square root of the ball stiffness and mass. Over the practical range of ball speed, mass, and stiffness, the force experienced by the head during football heading is mainly influenced by the speed of the ball rather than its mass or stiffness. The findings suggest that it would be more beneficial to develop player protection strategies that aim to reduce the speed at which the ball is traveling when headed by a player. Law changes reducing high ball speeds could be trialed at certain age grades or as a phased introduction to football heading.

Does ball carrier technique influence tackler head injury assessment risk in elite rugby union?

The aim of this study was to use video evidence of tackles in elite level rugby union to identify ball carrier proficiency characteristics, for both lower and upper body tackles, that have a higher propensity to result in Head Injury Assessments(HIA) for the tackler. HIA (n = 74) and non-HIA tackles (n = 233) were categorised as either front-on or side-on upper or lower body tackles and scored for ball carrying proficiency characteristics. Side-on tackles included tackles from behind. A Chi-Square test (p < 0.05) and Cramer's V were calculated to compare proficiency characteristics in HIA and non-HIA cases. For front-on upper body tackles, the ball carrier "fending into contact" (p < 0.01;ES = Moderate) and "explosiveness on contact" (p = 0.04;ES = Moderate) had a higher propensity to result in a HIA for the tackler. Fending into contact was exhibited in 47% of all upper body Tackle front-on HIA cases. The fending arm contacted the tackler's head in 67% of these cases. Fending into contact can potentially be dangerous and therefore emphasis should be placed on safe fending during tackle-based training drills. Referees should also be alert to arm-to-head contact during the fend. Given the low number of ball carrier characteristics identified, focus should be placed on tackler characteristics for HIA prevention strategies.

The effects of tackle height on inertial loading of the head and neck in Rugby Union: A multibody model analysis.

OBJECTIVE: There is evidence of chronic injury to the head-and-neck region of Rugby Union players. The aim of this study was to use multibody simulations to examine the effects of tackle height on both Tackler and Ball Carrier head kinematics and neck dynamics. RESEARCH DESIGN: Quantitative Exploratory Study Methods and procedures: 45 front-on shoulder tackles with no direct contact to the head/neck were simulated with the MADYMO pedestrian model and used to assess differences between upper body tackles and lower body tackles. The average resultant head linear and angular accelerations as well as neck forces and moments were assessed. MAIN OUTCOMES AND RESULTS: Much higher Ball Carrier head kinematic values and neck loading were predicted for upper body tackles compared to lower body tackles, and principal findings were unaffected by a sensitivity analysis. Tackler results were less straightforward and trends were influenced by the sensitivity analysis for muscle activation. CONCLUSION: Although further model validation is required, the results of this study indicate the need for further research on tackle heights and inertial head-and-neck loading in the tackle phase of play in Rugby Union.

Risks associated with significant head impact events in elite rugby union.

PRIMARY OBJECTIVES: To conduct video and statistical analysis on Rugby Union play, focusing mainly on the tackle, to establish the player to player configurations for significant direct head impacts and non-direct head impacts. RESEARCH DESIGN: Quantitative, observational cohort study. METHODS AND PROCEDURES: Video analysis of 52 significant direct head impacts (31 Tackle, 10 Ruck, 7 Dive and 4 Ground) and 40 non-direct head impact tackles from 2014/15 International Rugby Union matches. Relative risk, 95% CI and p-values were calculated for a range of tackle variables. MAIN OUTCOME AND RESULTS: Upper body tackles and lower body tackles accounted for 37% (19) and 23% (12) of cases, respectively, with the tackler as the head impacted player for 97% (30) of cases. The majority (81%) of tackle-related significant direct head impacts occurred in the second half of the game, with 63% of upper body tackle significant direct head impacts occurring in the final quarter. Tackler head placement and high speed tackles had statistical significance for causing tackle related significant direct head impacts as well as foot planting and difference in tackler and ball carrier mass for upper body tackles and ball carrier change in direction for lower body tackles. CONCLUSION: Tackle variables that statistically increased the risk of significant direct head impact were identified, which can aid player protection strategies.

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 < 0.001) and 4% (p = 0.007), respectively. Median head kinematics for all contact event categories appeared similar with no pairwise comparison resulting in statistical significance (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.

Can tackle height influence head injury assessment risk in elite rugby union?

OBJECTIVES: Tackle height laws are an area of controversy in rugby union. It is reported that the tackler is at most risk of a Head Injury Assessment (HIA). Therefore, the aim of this study was to use match video evidence of tackles in elite level rugby union to examine the effect of tackle heights on HIA risk for the tackler. DESIGN: Qualitative observational case-control study. METHODS: Each HIA (n=74) and control tackle (n=965) was categorised based on tackle direction (front- or side-on), tackle type (arm, shoulder or smother) and tackle height (upper trunk, mid-trunk, lower trunk, upper leg or lower leg). The Relative Risk (RR), 95% Confidence Interval (CI) and probability (p) values were calculated for each tackle height. RESULTS: Intended primary contact at the upper trunk of the ball carrier had a greater propensity to result in a HIA for the tackler for front-on upper body shoulder tackles (RR=1.48; 95%CI=1.16-1.90; p<0.01) and side-on upper body smother tackles (RR=2.30; 95%CI=1.82-2.92; p<0.01). Intended primary contact at the upper leg of the ball carrier had a greater propensity to result in a HIA for the tackler for front-on (RR=2.60; 95%CI=1.70-3.97; p<0.01) and side-on (RR=3.34; 95%CI=1.65-6.79; p<0.01) lower body shoulder tackles. CONCLUSIONS: To reduce tackler HIA risk, the results suggest tackling below the upper trunk for upper body tackles. The results also suggest tackling at the lower trunk for lower body tackles and avoiding the upper legs. Prevention strategies should place emphasis on tackling lower risk body regions such as the mid- and lower trunk.

Could lowering the tackle height in rugby union reduce ball carrier inertial head kinematics?

There is mounting evidence of reduced long-term cognitive ability in rugby players, even in those without a reported history of concussion. The tackle height law is an area of controversy. However, little is known about the effects of repetitive inertial head loading in rugby. Furthermore, the magnitude and influencing factors for head kinematics are generally unknown. In this exploratory study, 45 multibody front-on shoulder tackles simulated with the MADYMO pedestrian model and 20 staged rugby tackles executed by professional rugby players in a marker-based 3D motion laboratory were used to assess the effect of tackle height on ball carrier head kinematics. The peak resultant head linear accelerations, angular accelerations and change in angular velocities were measured and examined. The results suggest that tackle height strongly affects the head kinematics experienced by the ball carrier. In particular, higher ball carrier head kinematic values were identified for upper trunk tackles compared to mid/lower trunk tackles in both the multibody simulations and the staged rugby tackles. Average ball carrier peak resultant head linear acceleration, angular acceleration and change in angular velocity values for upper trunk tackles were greater than for mid/lower trunk tackles by a factor of 1.5, 2.5 and 1.7, in the multibody simulations, respectively, and 1.8 (p = 0.102), 2.2 (p = 0.025) and 2.3 (p = 0.004), in the staged tackles, respectively. The results of the study support the proposition of lowering the current tackle height laws to below the chest.

The Effect of Tackler Technique on Head Injury Assessment Risk in Elite Rugby Union.

PURPOSE: This study aimed to use match video evidence of tackles in elite-level rugby union to identify tackler proficiency characteristics, for both lower body and upper body tackles, that result in head injury assessments (HIA) for the tackler. METHODS: A review of international rugby union matches (2013-2017) and Pro 12/European Rugby Champions Cup matches (2014-2017) from a professional rugby union club was conducted. HIA (n = 74) and non-HIA tackles (n = 233) were categorized as either front-on or side-on upper body or lower body tackles and were scored for tackling proficiency characteristics. A chi-square test (P < 0.05) and phi and Cramer's V were calculated to compare HIA and non-HIA tackling proficiency characteristics. RESULTS: In both front- and side-on upper body and lower body tackles, "head up and forward/face up" and "head placement on correct side of ball carrier" were identified as having a lower propensity to result in an HIA for the tackler. For both front-on and side-on upper body tackles, "identify/track ball carrier onto shoulder" and "shortening steps" were identified. In addition, "straight back, centre of gravity forward of support base" and "identify/track ball carrier onto shoulder" were identified for front-on and side-on lower body tackles, respectively. CONCLUSIONS: This study identified tackle characteristics that had a lower propensity to result in an HIA for the tackler in both front-on and side-on upper body and lower body tackles.

Does player time-in-game affect tackle technique in elite level rugby union?

OBJECTIVES: It has been hypothesised that fatigue may be a major factor in tackle-related injury risk in rugby union and hence more injuries occur in the later stages of a game. The aim of this study is to identify changes in ball carrier or tackler proficiency characteristics, using elite level match video data, as player time-in-game increases. DESIGN: Qualitative observational cohort study. METHODS: Three 2014/15 European Rugby Champions Cup games were selected for ball carrier and tackler proficiency analysis. Analysis was only conducted on players who started and remained on the field for the entire game. A separate analysis was conducted on 10 randomly selected 2014/15 European Rugby Champions Cup/Pro 12 games to assess the time distribution of tackles throughout a game. A Chi-square test and one-way way ANOVA with post-hoc testing was conducted to identify significant differences (p<0.05) for proficiency characteristics and tackle counts between quarters in the game, respectively. RESULTS: Player time-in-game did not affect tackle proficiency for both the ball carrier and tackler. Any results that showed statistical significance did not indicate a trend of deterioration in proficiency with increased player time-in-game. The time distribution of tackles analysis indicated that more tackles occurring in the final quarter of the game than the first (p=0.04) and second (p=<0.01). CONCLUSIONS: It appears that player time-in-game does not affect tackler or ball carrier tackle technique proficiency at the elite level. More tackles occurring in the final quarter of a game provides an alternative explanation to more tackle-related injuries occurring at this stage.

Assessment of model-based image-matching for future reconstruction of unhelmeted sport head impact kinematics.

Player-to-player contact inherent in many unhelmeted sports means that head impacts are a frequent occurrence. Model-Based Image-Matching (MBIM) provides a technique for the assessment of three-dimensional linear and rotational motion patterns from multiple camera views of a head impact event, but the accuracy is unknown for this application. The goal of this study is to assess the accuracy of the MBIM method relative to reflective marker-based motion analysis data for estimating six degree of freedom head displacements and velocities in a staged pedestrian impact scenario at 40 km/h. Results showed RMS error was under 20 mm for all linear head displacements and 0.01-0.04 rad for head rotations. For velocities, the MBIM method yielded RMS errors between 0.42 and 1.29 m/s for head linear velocities and 3.53-5.38 rad/s for angular velocities. This method is thus beneficial as a tool to directly measure six degree of freedom head positional data from video of sporting head impacts, but velocity data is less reliable. MBIM data, combined in future with velocity/acceleration data from wearable sensors could be used to provide input conditions and evaluate the outputs of multibody and finite element head models for brain injury assessment of sporting head impacts.