Background: The use of video review to document visible signs (VS) of sport-related concussion in the National Football League (NFL) is a novel method to recognize head injuries. Hypothesis/Purpose: The current pilot studies used varying methodologies to (1) examine the frequency of VS in concussed NFL players using the Australian Football League's (AFL) checklist, and (2) assess the reliability of VS between non-expert and expert raters. Study design: Cohort study Methods: In the first pilot study, two non-expert raters rated VS of SRC occurring in the 2015 NFL season (n = 96) using a single VS from the AFL checklist. Based on this pilot study, two expert raters then rated VS of SRC during the 2017 NFL season (n = 211) using all VS from the AFL checklist. The frequency, total percent agreement (TPA), and reliability (kappa coefficients) were calculated for all VS of concussion for the two seasons. Kappa agreement was classified as fair (.41-.60), moderate (.61-.80), or substantial (.81-1.00). Significance was set at p .05. Results: The most frequent VS of concussion identified by both non-expert and expert raters were no behavior observed, slow to get up, and motor incoordination. The least frequent VS were impact seizure, blank/vacant look, and facial injury. For non-expert raters, the average TPA for VS ranged from 84% to 100% and kappa coefficients ranged from .52 to .68. For expert raters, the average TPA ranged from 83% to 100%, and kappa coefficients ranged from .56 to .86. Conclusion: In these preliminary analyses, use of multiple VS was a superior methodology, and the reliability of VS rating was stronger for experts. Due to the inherent differences in gameplay and protective equipment used in the NFL compared to other professional sports, it is our hope these data can generate new ways to improve existing practices and identify potentially novel VS of SRC.

Consideration of position-specific features of the NFL concussion environment could enable improved risk mitigation through the design of position-specific helmets to improve self-protection as well as protection for the other player with whom the contact occurs. The purpose of this paper is to quantify position-specific features of scenarios resulting in concussions to NFL players, and the players they contact, by reviewing all game footage (broadcast and non-broadcast) over 4 seasons. Position-specific features were documented for 647 concussions in which a primary exposure could be visualized, including impact source, helmet impact location, activity, and the other player with whom the contact occurred. Findings include the over-representation of helmet-to-ground impacts to the rear of the quarterback’s helmet, the high frequency of impacts to the side (upper) location of both concussed players and the players they contacted regardless of position, and distinct differences in the circumstances of concussions to cornerbacks and safeties. The study shows that some features of concussion scenarios are common to all positions, but several position-specific features exist and can inform the design of position-specific helmets for NFL players.

Wearable sensors that accurately record head impacts experienced by athletes during play can enable a wide range of potential applications including equipment improvements, player education, and rule changes. One challenge for wearable systems is their ability to discriminate head impacts from recorded spurious signals. This study describes the development and evaluation of a head impact detection system consisting of a mouthguard sensor and machine learning model for distinguishing head impacts from spurious events in football games. Twenty-one collegiate football athletes participating in 11 games during the 2018 and 2019 seasons wore a custom-fit mouthguard instrumented with linear and angular accelerometers to collect kinematic data. Video was reviewed to classify sensor events, collected from instrumented players that sustained head impacts, as head impacts or spurious events. Data from 2018 games were used to train the ML model to classify head impacts using kinematic data features (127 head impacts; 305 non-head impacts). Performance of the mouthguard sensor and ML model were evaluated using an independent test dataset of 3 games from 2019 (58 head impacts; 74 non-head impacts). Based on the test dataset results, the mouthguard sensor alone detected 81.6% of video-confirmed head impacts while the ML classifier provided 98.3% precision and 100% recall, resulting in an overall head impact detection system that achieved 98.3% precision and 81.6% recall.

Approximately 1.6-3.8 million sports-related traumatic brain injuries occur each year in the U.S. Researchers track the head motion using a variety of techniques to study the head injury biomechanics. To understand how helmets provide head protection, quantification of the relative motion between the head and the helmet is necessary. The purpose of this study was to compare helmet and head kinematics and quantify the relative motion of helmet with respect to head during experimental representations of on-field American football impact scenarios. Seven helmet-to-helmet impact configurations were simulated by propelling helmeted crash test dummies into each other. Head and helmet kinematics were measured with instrumentation and an optical motion capture system. The analysis of results, from 10 ms prior to the helmet contact to 20 ms after the loss of helmet contact, showed that the helmets translated 12-41mm and rotated up to 37 deg with respect to the head. The peak resultant linear acceleration of the helmet was about 2-5 times higher than the head. The peak resultant angular velocity of the helmet ranged from 37% less to 71% more than the head, depending on the impact conditions. The results of this study demonstrate that the kinematics of the head and the helmet are noticeably different and that the helmet rotates significantly with respect to the head during impacts. Therefore, capturing the helmet kinematics using a video motion tracking methodology is not sufficient to study the biomechanics of the head. Head motion must be measured independently of the helmet.

Professional American football games are recorded in digital video with multiple cameras, often at high resolution and high frame rates. The purpose of this study was to evaluate the accuracy of a videogrammetry technique to calculate translational and rotational helmet velocity before, during and after a helmet impact. In total, 10 football impacts were staged in a National Football League (NFL) stadium by propelling helmeted 50th percentile male crash test dummies into each other or the ground at speeds and orientations representative of concussive impacts for NFL players. The tests were recorded by experienced sports film crews to obtain video coverage and quality typically available for NFL games. A videogrammetry procedure was used to track the position and rotation of the helmet throughout the relevant time interval of the head impact. Compared with rigidly mounted retroreflective marker three dimensional (3-D) motion tracking that was concurrently collected in the experiments, videogrammetry accurately calculated changes in translational and rotational velocity of the helmet using high frame rate (two cameras at 240 Hz) video (7% and 15% error, respectively). Low frame rate (2 cameras at 60 Hz) video was adequate for calculating pre-impact translational velocity but not for calculating the translational or rotational velocity change of the helmet during impact.

Background: Concussions in American football remain a high priority of sports injury prevention programs. Detailed video review provides important information on causation, the outcomes of rule changes, and guidance on future injury prevention strategies. Purpose: Documentation of concussions sustained in National Football League games played during the 2015-2016 and 2016-2017 seasons, including consideration of video views unavailable to the public. Study Design: Descriptive epidemiology study. Methods: All reported concussions were reviewed with all available video footage. Standardized terminology and associated definitions were developed to describe and categorize the details of each concussion. Results: Cornerbacks sustained the most concussions, followed by wide receivers, then linebackers and offensive linemen. Half (50%) of concussions occurred during a passing play, 28% during a rushing play, and 21% on a punt or kickoff. Tackling was found to be the most common activity of concussed players, with the side of the helmet the most common helmet impact location. The distribution of helmet impact source—the object that contacted the concussed player’s helmet—differed from studies of earlier seasons, with a higher proportion of helmet-to-body impacts (particularly shoulder) and helmet-to-ground impacts and with a lower proportion of helmet-to-helmet impacts. Helmet-to-ground concussive impacts were notable for the high prevalence of impacts to the back of the helmet and their frequency during passing plays. Conclusion: Concussion causation scenarios in the National Football League have changed over time. Clinical Relevance: The results of this study suggest the need for expanded evaluation of concussion countermeasures beyond solely helmet-to-helmet test systems, including consideration of impacts with the ground and with the body of the opposing player. It also suggests the possibility of position-specific countermeasures as part of an ongoing effort to improve safety.

Background: Foot and ankle injuries are common in sports, particularly in cleated athletes. Traditionally, the athletic shoe has not been regarded as a piece of protective equipment but rather as a part of the uniform, with a primary focus on performance and subjective feedback measures of comfort. Changes in turf and shoe design have poorly understood implications on the health and safety of players. Evidence Acquisition: A literature search of the MEDLINE and PubMed databases was conducted. Keywords included athletic shoewear, cleated shoe, football shoes, and shoewear, and search parameters were between the years 2000 and 2016. Study Design: Clinical review. Level of Evidence: Level 5. Results: The athletic shoe is an important piece of protective sports equipment. There are several important structural considerations of shoe design, including biomechanical compliance, cleat and turf interaction, and shoe sizing/fit, that affect the way an athlete engages with the playing surface and carry important potential implications regarding player safety if not understood and addressed. Conclusion: Athletic footwear should be considered an integral piece of protective equipment rather than simply an extension of the uniform apparel. More research is needed to define optimal shoe sizing, the effect that design has on mechanical load, and how cleat properties, including pattern and structure, interact with the variety of playing surfaces.

OBJECTIVE:This study was designed to evaluate the performance of a pelvic restraint cushion (PRC), a submarining countermeasure that deploys under the thighs when a crash is detected in order to block the forward motion of the pelvis.METHODS:Sled tests approximating low- and high-speed frontal impacts were conducted with 4 female postmortem human subjects (PMHS) restrained by a lap and shoulder belt in the right front passenger seat. The subjects were tested with and without a PRC.RESULTS:The PRC is effective in reducing forward motion of the PMHS pelvis and reduces the risk of injury due to lap belt loading in a high-speed frontal crash.CONCLUSIONS:Although small sample size limits the utility of the study's findings, the results suggest that the PRC can limit pelvic forward motion and that pelvic injury due to PRC deployment is not likely.

Objectives: The 2 objectives of this study are to (1) examine the rib and sternal fractures sustained by small stature elderly females in simulated frontal crashes and (2) determine how the findings are characterized by prior knowledge and field data.Methods: A test series was conducted to evaluate the response of 5 elderly (average age 76 years) female postmortem human subjects (PMHS), similar in mass and size to a 5th percentile female, in 30 km/h frontal sled tests. The subjects were restrained on a rigid planar seat by bilateral rigid knee bolsters, pelvic blocks, and a custom force-limited 3-point shoulder and lap belt. Posttest subject injury assessment included identifying rib cage fractures by means of a radiologist read of a posttest computed tomography (CT) and an autopsy. The data from a motion capture camera system were processed to provide chest deflection, defined as the movement of the sternum relative to the spine at the level of T8.A complementary field data investigation involved querying the NASS-CDS database over the years 1997-2012. The targeted cases involved belted front seat small female passenger vehicle occupants over 40years old who were injured in 25 to 35 km/h delta-V frontal crashes (11 to 1 o'clock).Results: Peak upper shoulder belt tension averaged 1,970N (SD = 140 N) in the sled tests. For all subjects, the peak x-axis deflection was recorded at the sternum with an average of -44.5mm or 25% of chest depth. The thoracic injury severity based on the number and distribution of rib fractures yielded 4 subjects coded as Abbreviated Injury Scale (AIS) 3 (serious) and one as AIS 5 (critical). The NASS-CDS field data investigation of small females identified 205 occupants who met the search criteria. Rib fractures were reported for 2.7% of the female occupants.Conclusions: The small elderly test subjects sustained a higher number of rib cage fractures than expected in what was intended to be a minimally injurious frontal crash test condition. Neither field studies nor prior laboratory frontal sled tests conducted with 50th percentile male PMHS predicted the injury severity observed. Although this was a limited study, the results justify further exploration of the risk of rib cage injury for small elderly female occupants.

This study evaluated the biofidelity of the WorldSID and the ES-2re under whole-body side impact conditions with and without a side airbag using the biomechanical cadaveric response data generated from 4.3m/s whole-body side impact tests. Impact forces, spinal kinematics, and chest deflections were considered in the biofidelity evaluation. Average responses and response corridors of PMHS were created using a time-alignment technique to reduce variability of the PMHS responses while maintaining the sum of the time shifts to be zero for each response. Biofidelity of the two dummies was compared using a correlation and analysis (CORA) method. The WorldSID demonstrated better biofidelity than the ES-2re in terms of CORA ratings in the conditions with airbag (0.53 vs. 0.46) and without an airbag (0.57 vs. 0.49). Lastly, the kinematic analysis of the two dummies indicated an overly compliant shoulder response of the WorldSID and excessive forward rotation of the ES-2re relative to the PMHS.

In American football, hyper-dorsiflexion of the first metatarsophalangeal (first MTP) joint is the predominant mechanism of first MTP joint sprains (turf toe). The risk of acute first MTP joint sprain has been found to increase as first MTP joint angle increases. The bending resistance of the shoe dictates the proportion of an externally applied load that can be passed into the shoe (i.e. not through the first MTP joint) and thus may influence the magnitude of flexion imparted to the first MTP joint and hence the risk of injury. The current study introduces the Football American Shoe Tester (FAST), a flexion apparatus designed to measure the bending resistance of American football shoes at angles of forefoot dorsiflexion from 15 degrees to 75 degrees. The FAST was used to quantify the forefoot bending behaviour of a range of American football shoes. Thirty different models of US size 12 shoes were tested. Linearized bending stiffness ranged from 0.27 to 0.8 Nm/deg, while peak torque ranged from 11.8 to 25.5 N m. The testing revealed characteristic differences in torque-angle response across shoe models and quantified the extent of shoe stiffening at angles of dorsiflexion beyond those studied in the past.

Among the three GRF cushioning variables, maximum LR is recommended for evaluating heel cushioning performance, as suggested by its better agreement with mechanical impact scores. Tibial acceleration seems to be effective in differentiating shoe of varying mechanical heel impact scores during higher loading intensity. Further investigation on mechanical impact score with different loading intensities should be done to help footwear manufacturer in the design of cushioning evaluation protocol. Forefoot and rearfoot loading biomechanics should be better differentiated to explore the underlying shock attenuation mechanism of different shoe-subject interfaces and in different force intensities.

In American football, hyper-dorsiflexion of the first metatarsophalangeal (1 MTP) joint is the predominant mechanism of 1 MTP sprains (turf toe). The risk of acute 1 MTP sprain has been found to increase as 1 MTP angle increases. The bending resistance of the shoe dictates the proportion of an externally applied load that can be passed into the shoe (i.e., not through the 1 MTP joint) and thus influences the magnitude of flexion imparted to the 1 MTP joint. This study quantified the forefoot bending resistance of a range of cleated American football shoes. A total of 21 pairs of size 12 shoes were dynamically tested over flexion angles from 30° to 90°. Bending stiffness ranged from 0.10 to 0.35 Nm/deg, while peak torque ranged from 5.1 to 16.6 Nm. The relationship between torque and flexion angle was nearly linear for all of the shoes tested and the peak torque values were substantially lower than 1 MTP joint moments that have been measured in the human foot during athletic activities. These results suggest that an opportunity exists to better balance athletic performance and acute 1 MTP joint injury risk by incorporating non-linearity into the torque-angle characteristic of football cleats, such that the proportion of external load borne by the shoe increases at flexion angles above 60°.

To serve as tools for assessing injury risk, the biofidelity of whole-body pedestrian impact dummies should be validated against reference data from full-scale pedestrian impact tests. To facilitate such evaluations, a simplified generic vehicle-buck has been recently developed that is designed to have characteristics representative of a generic small sedan. Three 40 km/h pedestrian-impact tests have been performed, wherein Post Mortem Human Surrogates (PMHS) were struck laterally in a mid-gait stance by the buck. Corridors for select trajectory measures derived from these tests have been published previously. The goal of this study is to act as a companion dataset to that study, describing the head velocities, body region accelerations (head, spine, pelvis, lower extremities), angular velocities, and buck interaction forces, and injuries observed during those tests. Scaled, transformed head accelerations exceeded 80 g prior to head contact with the windshield for two of the three tests. Head xaxis angular velocity exceeded 40 rad/s prior to head contact for all three tests. In all cases the peak resultant head velocity relative to the vehicle was greater than the initial impact speed of the vehicle. Corridors of resultant head velocity relative to the vehicle were also developed, bounded by the velocities observed in these tests combined with those predicted to occur if the PMHS necks were perfectly rigid. These results, along with the other kinematic and kinetic data presented, provide a resource for future pedestrian dummy development and evaluation.

This study quantified the mechanical interactions between an American football cleat and eight surfaces used by professional American football teams. Loading conditions were applied with a custom-built testing apparatus designed to represent play-relevant maneuvers of elite athletes. Two natural grass and six infill artificial surfaces were tested with the cleated portion of a shoe intended for use on either surface type. In translation tests with a 2.8-kN vertical load, the grass surfaces limited the horizontal force on the cleats by tearing. This tearing was not observed with the artificial surfaces, which allowed less motion and generated greater horizontal force (3.2kN vs. 4.5kN, p<0.05). Similarly, rotation tests generated less angular displacement and greater torque on the artificial surfaces (145Nm vs. 197Nm, p<0.05). Translation/drop tests, in which the foot-form was launched into the surfaces with both horizontal and vertical velocity components generated less peak horizontal force on the natural surfaces than on the artificial surfaces (2.4kN vs. 3.0kN, p<0.05). These results suggest a force-limiting mechanism inherent to natural grass surfaces. Future work should consider implications of these findings for performance and injury risk and should evaluate the findings' sensitivity to cleat pattern and playing conditions.

The development of advanced injury prediction models requires biomechanical and injury tolerance information for all regions of the body. While numerous studies have investigated injury mechanics of the thorax under frontal impact, there remains a dearth of information on the injury mechanics of the torso under blunt impact to the back. A series of hub-impact tests were performed to the back surface of the mid-thorax of four mid-size male cadavers. Repeated tests were performed to characterize the biomechanical and injury response of the thorax under various impact speeds (1.5m/s, 3m/s and 5.5m/s). Deformation of the chest was recorded with a 59-gage chestband. Subject kinematics were also recorded with a high-speed optoelectronic 3D motion capture system. In the highest-severity tests, peak impact forces ranged from 6.9 to 10.5kN. The peak change in extension angle measured between the 1st thoracic vertebra and the lumbar spine ranged from 39 to 62°. The most commonly observed injuries were strains of the costovertebral/costotransverse joint complexes, rib fractures, and strains of the interspinous and supraspinous ligaments. The majority of the rib fractures occurred in the rib neck between the costovertebral and costotransverse joints. The prevalence of rib-neck fractures suggests a novel, indirect loading mechanism resulting from bending moments generated in the rib necks caused by motion of the spine. In addition to the injury information, the biomechanical responses quantified here will facilitate the future development and validation of human body models for predicting injury risk during impact to the back.

This study quantified the mechanical interactions of 19 American football cleats with a natural grass and an infill-type artificial surface under loading conditions designed to represent play-relevant manoeuvres of elite athletes. Variation in peak forces and torques was observed across cleats when tested on natural grass (2.8–4.2 kN in translation, 120–174 Nm in rotation). A significant (p < 0.05) relationship was found between the peak force and torque on natural grass. Almost all of the cleats caused shear failure of the natural surface, which generated a divot following a test. This is a force-limiting cleat release mode. In contrast, all but one of the cleat types held fast in the artificial turf, resulting in force and torque limited by the prescribed input load from the test device (nom. 4.8 kN and 200 Nm). Only one cleat pattern, consisting of small deformable nubs, released on the artificial surface and generated force (3.9 kN) comparable to the range observed with natural grass. These findings (1) should inform the design of cleats intended for use on natural and artificial surfaces and (2) suggest a mechanical explanation for a higher lower-limb injury rate in elite athletes playing on artificial surfaces.

Efforts to develop a dummy capable of assessing injury risk in a pedestrian collision require biofidelity assessment targets in full‐scale pedestrian‐impact scenarios. The goal of this study was to develop trajectory analysis methods and kinematic biofidelity corridors for 50th percentile male adults subjected to 40 km/h pedestrian impacts using a recently‐developed generic sedan buck. Tests were performed with three male post‐mortem human surrogates initially positioned to be struck laterally in a mid‐gait stance. The kinematics of the post‐mortem human surrogates were recorded via high‐speed video imagers and a three-dimensional (3D) optoelectronic motion capture system. Trajectories of the head center of gravity, T1, T8, and the pelvis were digitized via a two-dimensional (2D) video (up to the time of head impact). The 2D trajectory data were verified against comparable measures from the 3D motion tracking system. These data were then scaled to a 50th percentile adult male and corridors for the scaled trajectories were developed. Combined with the generic vehicle buck and validated trajectory capture and analysis methods, these results provide a means to evaluate the whole body kinematic biofidelity of 50th percentile male pedestrian dummies and computational models in perpetuity.

The effect of posture and subject-specific factors on injury outcome is an active field of research in injury biomechanics, in particular in automotive safety research where post-mortem human subjects (PMHS) are used as surrogates. Current PMHS tests routinely include acquisition of the subjects׳ geometry and kinematics. However, combining these two datasets to better understand the injury mechanism is still a challenge. This study investigated the connection between pre-impact posture and resulting injuries in six previously published side impact sled tests (three with a rigid wall and three with an airbag) by creating three-dimensional kinematic animations (3DKA) of the tests. The 3DKA allow qualitative assessment of parameters related to posture and their possible effect on injury outcome. The orientation of the struck scapula and the lateral leaning of the torso were identified as potentially significant parameters. The ranges of variation in these parameters were quantified and compared to the number of rib fractures for each subject: the data suggested a correlation, but there was insufficient data for a probabilistic analysis. The 3DKA were published with this study and are freely available.