Consensus Head Acceleration Measurement Practices (CHAMP): Origins, Methods, Transparency and Disclosure.

The use of head kinematic measurement devices has recently proliferated owing to technology advances that make such measurement more feasible. In parallel, demand to understand the biomechanics of head impacts and injury in sports and the military has increased as the burden of such loading on the brain has received focused attention. As a result, the field has matured to the point of needing methodological guidelines to improve the rigor and consistency of research and reduce the risk of scientific bias.

Best Practices for Conducting Physical Reconstructions of Head Impacts in Sport.

Physical reconstructions are a valuable methodology for quantifying head kinematics in sports impacts. By recreating the motion of human heads observed in video using instrumented test dummies in a laboratory, physical reconstructions allow for in-depth study of real-world head impacts using well-established surrogates such as the Hybrid III crash test dummy. The purpose of this paper is to review all aspects of the physical reconstruction methodology and discuss the advantages and limitations associated with different choices in case selection, study design, test surrogate, test apparatus, text matrix, instrumentation, and data processing.

Laboratory Evaluation of Shell Add-On Products for American Football Helmets for Professional Linemen.

The Guardian Cap NXT (GC NXT) and the ProTech Helmet Cap (ProTech) are commercially available aftermarket products designed to augment the energy attenuation characteristics of American football helmets. The ability of these helmet shell add-on products to mitigate the severity of impacts typically experienced by professional offensive and defensive linemen was evaluated for seven helmet models using two test series. In linear impactor tests, the GC NXT reduced head impact severity as measured by the head acceleration response metric (HARM) by 9% relative to the helmets only, while the ProTech reduced HARM by 5%.

Position-Specific Circumstances of Concussions in the NFL: Toward the Development of Position-Specific Helmets.

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.

Development and Evaluation of a Test Method for Assessing the Performance of American Football Helmets.

As more is learned about injury mechanisms of concussion and scenarios under which injuries are sustained in football games, methods used to evaluate protective equipment must adapt. A combination of video review, videogrammetry, and laboratory reconstructions was used to characterize concussive impacts from National Football League games during the 2015-2017 seasons. Test conditions were generated based upon impact locations and speeds from this data set, and a method for scoring overall helmet performance was created.

Comparison of Laboratory and On-Field Performance of American Football Helmets.

The relationship between laboratory and on-field performance of football helmets was assessed for 31 football helmet models selected from those worn by players in the 2015-2019 National Football League (NFL) seasons. Linear impactor tests were conducted with helmets placed on an instrumented Hybrid III head and neck assembly mounted on a sliding table. Based on impacts to each helmet at six impact locations and three velocities, a helmet performance score (HPS) was calculated using a linear combination of the head injury criterion (HIC) and the diffuse axonal multi-axis general evaluation (DAMAGE).

Laboratory Reconstructions of Concussive Helmet-to-Helmet Impacts in the National Football League.

Seventeen concussive helmet-to-helmet impacts occurring in National Football League (NFL) games were analyzed using video footage and reconstructed by launching helmeted crash test dummies into each other in a laboratory. Helmet motion on-field and in the laboratory was tracked in 3D before, during, and after impact in multiple high frame rate video views. Multiple (3-10) tests were conducted for each of the 17 concussive cases (100 tests total) with slight variations in input conditions.

The Effect of Muscle Activation on Head Kinematics During Non-injurious Head Impacts in Human Subjects.

In this study, twenty volunteers were subjected to three, non-injurious lateral head impacts delivered by a 3.7 kg padded impactor at 2 m/s at varying levels of muscle activation (passive, co-contraction, and unilateral contraction). Electromyography was used to quantify muscle activation conditions, and resulting head kinematics were recorded using a custom-fit instrumented mouthpiece.

Video Analysis of Reported Concussion Events in the National Football League During the 2015-2016 and 2016-2017 Seasons.

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.

Inertial Properties of Football Helmets.

The inertial properties of a helmet play an important role in both athletic performance and head protection. In this study, we measured the inertial properties of 37 football helmets, a National Operating Committee on Standards for Athletic Equipment (NOCSAE) size 7¼ headform, and a 50th percentile male Hybrid III dummy head. The helmet measurements were taken with the helmets placed on the Hybrid III dummy head.

A reanalysis of football impact reconstructions for head kinematics and finite element modeling.

Background: Head kinematics generated by laboratory reconstructions of professional football helmet impacts have been applied to computational models to study the biomechanics of concussion. Since the original publication of this data, techniques for evaluating accelerometer consistency and error correction have been developed. This study applies these techniques to the original reconstruction data and reanalyzes the results given the current state of concussion biomechanics.

Kinematics and kinetics of vigorous head shaking.

Previous studies on neck muscle strength and motion have assumed or imposed varying constraints on the heads and bodies of the subjects. In this study, we asked 20 subjects to vigorously shake their heads 5-10 times in a completely unconstrained manner. The kinematics and kinetics of the head and neck were measured from video analysis and instrumentation mounted inside the mouth.

Factors affecting ejection risk in rollover crashes.

Ejection greatly increases the risk of injury and fatality in a rollover crash. The purpose of this study was to determine the crash, vehicle, and occupant characteristics that affect the risk of ejection in rollovers. Information from real world rollover crashes occurring from 2000 - 2010 was obtained from the National Automotive Sampling System (NASS) in order to analyze the effect of the following parameters on ejection risk: seatbelt use, rollover severity, vehicle type, seating position, roof crush, side curtain airbag deployment, glazing type, and occupant age, gender, and size.

Injuries caused by brake pedal loading of the midfoot.

In a frontal car crash, the driver’s foot and ankle may be injured due to loading by the brake pedal. The driver of a vehicle often has time to initiate emergency braking before an impending collision, which places the forefoot or midfoot over the brake pedal. During the crash, the pedal may induce dorsiflexion and axial loading of the ankle due to forward motion of the occupant and rearward intrusion of the pedal relative to the vehicle.

Validation of concussion risk curves for collegiate football players derived from HITS data.

For several years, Virginia Tech and other schools have measured the frequency and severity of head impacts sustained by collegiate American football players in real time using the Head Impact Telemetry (HIT) System of helmet-mounted accelerometers. In this study, data from 37,128 head impacts collected at Virginia Tech during games from 2006 to 2010 were analyzed. Peak head acceleration exceeded 100 g in 516 impacts, and the Head Injury Criterion (HIC) exceeded 200 in 468 impacts.

Ankle injury mechanisms: lessons learned from cadaveric studies.

The biomechanics of ankle injury have been studied extensively, primarily through mechanical testing of human cadavers. Cadaveric testing is an invaluable methodology in biomechanics, because the magnitude and direction of the loading can be measured precisely and correlated with the resulting injury pattern. Clinical and epidemiological studies provide useful descriptions of injury patterns that occur in the real world, but their retrospective nature precludes a definitive analysis of the forces that caused the injury.

Head and neck loading in everyday and vigorous activities.

The purpose of this study was to document head and neck loading in a group of ordinary people engaged in non-injurious everyday and more vigorous physical activities. Twenty (20) volunteers that were representative of the general population were subjected to seven test scenarios: a soccer ball impact to the forehead, a self-imposed hand strike to the forehead, vigorous head shaking, plopping down in a chair, jumping off a step, a seated drop onto the buttocks, and a vertical drop while seated supine in a chair. Some scenarios involved prescribed and well-controlled stimuli, while others allowed the volunteers to perform common activities at a self-selected level of intensity.

Relationship between linear and rotational head acceleration in various activities.

Head injury is typically predicted using linear or rotational acceleration-based injury criteria. In many cases, the linear components of head acceleration can be determined more easily than the rotational components. Peak rotational head acceleration (apeak) can be calculated from the peak linear head acceleration (apeak) by assuming a value for the effective radius of rotation (r) of the head (apeak = apeak / r).

Effect of delta-V errors in NASS on frontal crash risk calculations.

The most important factor in predicting the risk of injury or death in a frontal crash is the crash severity, which is expressed as the velocity change, or delta-V, experienced by the vehicle during the crash. The National Automotive Sampling System (NASS) is the largest database in the world linking injury outcomes with delta-Vs, which are obtained from field reconstructions. The accuracy of these reconstructions was assessed by analyzing 228 NASS cases involving single event frontal crashes in which the vehicle's frontal delta-V was also measured directly by an onboard event data recorder (EDR).

The line of action in the tibia during axial compression of the leg.

Compression of the leg induces bending in the tibia, which can lead to tensile failure of the bone in the midshaft. The purpose of this study was to determine the orientation of the compressive load vector in the human tibia. Five cadaveric lower extremities were instrumented with in situ 6-axis tibial and fibular load cells and subjected to quasistatic axial leg compression tests in two knee positions and nine ankle positions.

The effects of axial preload and dorsiflexion on the tolerance of the ankle/subtalar joint to dynamic inversion and eversion.

Forced inversion or eversion of the foot is considered a common mechanism of ankle injury in vehicle crashes. The objective of this study was to model empirically the injury tolerance of the human ankle/subtalar joint to dynamic inversion and eversion under three different loading conditions: neutral flexion with no axial preload, neutral flexion with 2 kN axial preload, and 30 degrees of dorsiflexion with 2 kN axial preload. 44 tests were conducted on cadaveric lower limbs, with injury occurring in 30 specimens.

Calculation of tibial loading using strain gauges.

The standard methodology for measuring loads in long bones is the in situ load cell, which enables direct measurements, but alters the stiffness and mass of the subject bone. Bone loading can also be calculated by applying linear beam theory to measurements from strain gauges affixed to the bone surface. The efficacy of the strain gauge method was assessed in this study by mounting three strain gauge rosettes to the midshaft of the tibia in two cadaveric above-knee leg specimens.