Angular Acceleration Of Head Research Articles

Predicting head injury metrics during low- to moderate-speed frontal collisions using computational simulations

ObjectivesSubjective reports of mild traumatic brain injury (mTBI) are common following low-energy motor-vehicle collisions. Biomechanical analyses are useful in providing a quantitative means for determining the likelihood of sustaining mTBI. While occupant dynamics in low-speed rear impacts have been extensively investigated, peer-reviewed studies on occupant dynamics during low-speed frontal collisions are sparse. The objective of this study is to present a validated computational method to quantify the biomechanical response of the head in low- and moderate-speed frontal collisions. Data and methodsThis study used data from a previously-published series of four instrumented in-line front-to-rear staged collisions using 2014 Honda Accord sedans at closing velocities of approximately 7.4 kph (test L1), 12.7 kph (test L2), 21.7 kph (test L3), and 33.6 kph (test L4) kph. A model of the test vehicle occupant compartment was created using the MAthematical DYnamic MOdeling (MADYMO) software using methods previously described. Crash pulse data from L4 were applied to the MADYMO model. Seat belt parameters were optimized to achieve reasonable agreement between simulation results and test data for relevant head injury metrics (linear head acceleration [LHA], angular head acceleration [AHA], and HIC15). Crash pulses from the other tests in the series (L1, L2, and L3) were then applied to the model and peak values for LHA, AHA, and HIC15 were compared to the physical test data to demonstrate validation. ResultsThe optimization of seat belt and seat parameters within the MADYMO model resulted in accurate prediction of ATD dynamics demonstrated in Test L4. The simulation-predicted peak LHA was within 0.2 g of the test value, peak AHA was within 64 rad/s2, and HIC15 was within 0.46. When applied to the remainder of the tests (L1, L2, and L3), the optimized model showed excellent accuracy in predicting peak LHA and HIC15. When compared to the physical test data, the simulation-predicted values for LHA were within 0.4 g or less and the HIC15 values were within 0.4 or less across all tests. The model generally over-predicted AHA, particularly for the lower-severity collisions (L1 and L2). ConclusionsWe have demonstrated a reliable methodology for developing a biomechanical computational model to predict head injury metrics in low- to moderate-speed frontal collisions. This approach can be particularly valuable in forensic investigations of real-world crashes. Pre-existing crash test data can be used in conjunction with exemplar vehicle information to validate a MADYMO model. Appropriate crash pulse data from classical accident reconstruction techniques, event data recorders, or simulations can then be applied to the model to accurately predict head dynamics for real-world vehicle occupants without the need for full-scale staged crash tests.

VESTIBULAR IMPLANT STIMULATION PAUSE DETECTION THRESHOLDS: IMPLICATIONS FOR DESIGN OF BATTERY DEPLETION ALERTS.

Vestibular implants (VI) modulate the rate and amplitude of charge-balanced current pulses to encode head angular velocity or acceleration. When the battery of a VI becomes depleted, stimulation interruptions can cause vertigo. To avoid this, VIs can use alert signals such as vibration and beeping to remind the user to replace the battery. However, in distracting and noisy environments typical of activities of daily life, some patients may fail to hear or feel those alerts, so a physiological signal can be used as an alternate channel for signaling battery depletion. Pauses in the stimulation waveform can be delivered for this purpose, with the length of the pause long enough to be detected reliably by the patient but not so long as to induce dizziness or a vertigo attack. As a guide for the design of a physiologic battery depletion alert system, this study reports the ability of nine long-term, continuous VI users to detect stimulation pauses of various durations. We also show the effect of distraction on patients' detection thresholds and response latencies for detected events.

Padded Helmet Shell Covers in American Football: A Comprehensive Laboratory Evaluation with Preliminary On-Field Findings.

Protective headgear effects measured in the laboratory may not always translate to the field. In this study, we evaluated the impact attenuation capabilities of a commercially available padded helmet shell cover in the laboratory andon the field. In the laboratory, we evaluated the padded helmet shell cover's efficacy in attenuating impact magnitude across six impact locations and three impact velocities when equipped to three different helmet models. In a preliminary on-field investigation, we used instrumented mouthguards to monitor head impact magnitude in collegiate linebackers during practice sessions while not wearing the padded helmet shell covers (i.e., bare helmets) for one season and whilst wearing the padded helmet shell covers for another season. The addition of the padded helmet shell cover was effective in attenuating the magnitude of angular head accelerations and two brain injury risk metrics (DAMAGE, HARM) across most laboratory impact conditions, but did not significantly attenuate linear head accelerations for all helmets. Overall, HARM values were reduced in laboratory impact tests by an average of 25% at 3.5m/s (range: 9.7 to 39.6%), 18% at 5.5m/s (range: -5.5 to 40.5%), and 10% at 7.4m/s (range: -6.0 to 31.0%). However, on the field, no significant differences in any measure of head impact magnitude were observed between the bare helmet impacts and padded helmet impacts. Further laboratory tests were conducted to evaluate the ability of the padded helmet shell cover to maintain its performance after exposure to repeated, successive impacts and across a range of temperatures. This research provides a detailed assessment of padded helmet shell covers and supports the continuation of in vivo helmet research to validate laboratory testing results.

Influence of the frame of reference on head acceleration events recorded by instrumented mouthguards in community rugby players

ObjectivesTo highlight the need for standardisation in the communication of head impact telemetry from instrumented mouthguards (iMG). The purpose of this study is to examine how the frame of reference...

Driver Mental Fatigue Detection Based on Head Posture Using New Modified reLU-BiLSTM Deep Neural Network

Early detection of driver mental fatigue is one of the active areas of research in smart and intelligent vehicles. There are various methods, based on measuring the physiological characteristics of the driver utilising sensors and computer vision, proposed in the literature. In general, driver behaviour is unpredictable that can suddenly change the nature of driving and dynamics under mental fatigue. This results in sudden variations in driver body posture and head movement, with consequent inattentive behaviour that can end in fatal accidents and crashes. In the process of delineating the different driving patterns of driver states while active or influenced by mental fatigue, this paper contributes to advancing direct measurement approaches. In the novel approach proposed in this paper, driver mental fatigue and drowsiness are measured by monitoring driver’s head posture motions using XSENS motion capture system. The experiments were conducted on 15 healthy subjects on a MATHWORKS driver-in-loop (DIL) simulator, interfaced with Unreal Engine 4 studio. A new modified bidirectional long short-term memory deep neural network, based on a rectified linear unit layer, was designed, trained and tested on 3D time-series head angular acceleration data for sequence-to-sequence classification. The results showed that the proposed classifier outperformed state-of-art approaches and conventional machine learning tools, and successfully recognised driver’s active, fatigue and transition states, with overall training accuracy of 99.2%, sensitivity of 97.54%, precision and F1 scores of 97.38% and 97.46%, respectively. The limitations of the current work and directions for future work are also explored.

Tacklers' Head Inertial Accelerations Can Be Decreased by Altering the Way They Engage in Contact with Ball Carriers' Torsos.

ABSTRACTPurposeThis study aimed to investigate how four types of successfully executed, legal front-on, one-on-one torso tackles influence the tacklers’ and ball carriers’ inertial head kinematics.MethodsA total of 455 successful front-on, one-on-one torso tackle trials completed by 15 rugby code players using three-dimensional motion capture were recorded. Tackles differed with respects to the height of the contact point on the ball carrier’s torso. A series of mixed general linear models were conducted.ResultsThe tackler sustained the highest peak resultant linear (P < 0.001) and angular (P < 0.01) head accelerations when contacting the lower torso to execute a “dominant” tackle compared with mid or upper torso, although these latter tackle types had the lowest ball carrier inertial head kinematics. When executing a “smother” tackle technique, a significant decrease in peak resultant linear head acceleration was observed with a vertical “pop” then lock action used, compared with the traditional upper torso tackling technique (P < 0.001).ConclusionsModifying the tackler’s engagement with a ball carrier’s torso, with respect to height and technical execution, alters the inertial head kinematics of the tackler and the ball carrier. The traditional thinking about optimal tackle technique, as instructed, may need to be reevaluated, with the midtorso being a potential alternative target contact height, whereas changes in tackle execution may be relatively protective for tacklers when executing either a dominant or smother tackle. This study provides critical scientific evidence to underpin revised coaching tackling technique interventions that might enhance player safety. Tackles in which the tackler contacts the ball carrier around the midtorso region, rather than lower torso, produce the lowest acceleration and thus may contribute to reducing head injury risk for the tackler.

Traumatic brain injury risk assessment with smart technology

Mild traumatic brain injuries (mTBIs) continue to burden our warfighters. The high-tech industry has delivered wearable Micro-Electro-Mechanical System (MEMS) head-impact sensors to monitor impact forces. So far, these MEMS sensors have categorically failed to detect mTBIs and are therefore of no clinical utility for diagnosis. Our recent studies have shown that human head kinematics is anisotropic with respect to pitch–roll–yaw degrees of freedom of the head and neck. In the present project, we generated head acceleration datasets on non-injurious impacts and mTBI events based on mean values from the literature. We then augmented the simulated data with pitch–roll–yaw information followed by machine learning with a Classification and Regression Tree analysis. Our results revealed that head angular acceleration in pitch is the best predictor. More than 81.3 % of concussive injuries had head angular accelerations in pitch exceeding 3527 rad/s2. Out of 18.6% of concussive injuries with head angular accelerations in pitch under 3527 rad/s2, 75% of these cases had head angular accelerations in roll exceeding 1679 rad/s2. This study shows that artificial intelligence and machine learning should be able to provide accurate identification of subject-specific concussive thresholds in real time and in the field, thereby moving concussion diagnosis toward precision medicine.

Serum neurofilament light concentration does not increase following exposure to low velocity football heading

ABSTRACT Objectives: To investigate if heading frequency and impact biomechanics in a single session influence the concentration of serum neurofilament light (NF-L), a sensitive biomarker for axonal damage, up to 7 days after heading incident at ball velocities reflecting basic training drills. Methods: Forty-four males were randomized into either control (n = 8), 10 header (n = 12), 20 header (n = 12) or 40 header (n = 12) groups. Linear and angular head accelerations were quantified during heading. Venous blood samples were taken at baseline, 6 h, 24 h and 7 days after heading. Serum NF-L was quantified using Quanterix NF-L assay kit on the Simoa HD-1 Platform. Results: Serum NF-L did not alter over time (p = 0.44) and was not influenced by number of headers [p = 0.47; mean (95% CI) concentrations at baseline 6.00 pg · ml− 1 (5.00–7.00 pg · ml− 1); 6 h post 6.50 pg · ml−1 (5.70–7.29 pg · ml−1); 24 h post 6.07 pg · ml−1 (5.14–7.01 pg · ml− 1); and 7 days post 6.46 pg · ml−1 (5.45–7.46 pg · ml−1)]. There was no relationship between percentage change in NF-L and summed session linear and angular head accelerations. Conclusion: In adult men, heading frequency or impact biomechanics did not affect NF-L response during a single session of headers at ball velocities reflective of basic training tasks.

Concussion and the severity of head impacts in mixed martial arts.

Concern about the consequences of head impacts in US football has motivated researchers to investigate and develop instrumentation to measure the severity of these impacts. However, the severity of head impacts in unhelmeted sports is largely unknown as miniaturised sensor technology has only recently made it possible to measure these impacts in vivo. The objective of this study was to measure the linear and angular head accelerations in impacts in mixed martial arts, and correlate these with concussive injuries. Thirteen mixed martial arts fighters were fitted with the Stanford instrumented mouthguard (MiG2.0) participated in this study. The mouthguard recorded linear acceleration and angular velocity in 6 degrees of freedom. Angular acceleration was calculated by differentiation. All events were video recorded, time stamped and reported impacts confirmed. A total of 451 verified head impacts above 10g were recorded during 19 sparring events (n = 298) and 11 competitive events (n = 153). The average resultant linear acceleration was 38.0624.3g while the average resultant angular acceleration was 256761739 rad/s2. The competitive bouts resulted in five concussions being diagnosed by a medical doctor. The average resultant acceleration (of the impact with the highest angular acceleration) in these bouts was 86.7618.7g and 756163438 rad/s2. The average maximum Head Impact Power was 20.6kW in the case of concussion and 7.15kW for the uninjured athletes. In conclusion, the study recorded novel data for sub-concussive and concussive impacts. Events that resulted in a concussion had an average maximum angular acceleration that was 24.7% higher and an average maximum Head Impact Power that was 189% higher than events where there was no injury. The findings are significant in understanding the human tolerance to short-duration, high linear and angular accelerations.

Influences of impact scenarios and vehicle front-end design on head injury risk of motorcyclist

Motorcycle to vehicle collision is one of the most common accidents in the world and usually leads to serious or fatal head injuries to motorcyclists. This study aims to investigate the influences of impact scenarios and vehicle front-end design parameters on head injury risk of the motorcyclist. Five general vehicle types and different impact scenarios were selected for a parametric analysis. Impact scenarios were set according to ISO, 13232 regulation considering impact angles and impact speeds. Five vehicle types of Sedan, MPV (Multi-Purpose Vehicle), SUV (Sport Utility Vehicle), EV (Electric Vehicle) and 1-Box vehicle were included. HIC15 (Head Injury Criterion), head angular acceleration and CSDM (Cumulative Strain Damage Measure) were calculated to evaluate head injury risk of the motorcyclist. The results show that the critical impact speed for HIC15 and head angular acceleration was around 15 m/s, while the critical speed for CSDM was approximately 10 m/s. Impact angle of 45° show extremely high injury risk to the motorcyclist head. Bonnet leading edge height and its combination with other parameter present high influences on motorcyclist head injuries, and the increasing the bonnet leading edge height can potentially reduce head injury risk of motorcyclists. In summary, the present research results provide some theoretic bases for determining the test speed in motorcycle-vehicle crash regulation and design consideration for typical vehicle front end shape.

The Effect of Eight Weeks of Training on Head and Neck Stability in Tsuki Punch after Neck Muscle Fatigue

Introduction : Muscular fatigue can interfere with the proper functioning of postural stability strategies, hence decreasing stability and increasing the risk of injuries in athletes. The aim of this study is to examine the effect of training on head and neck stability against Tsuki punch during the neck muscle fatigue in male athletes. Materials and Methods: 24 professional male karate athletes were selected and randomly divided into the experimental [n = 12, age: 20.92 ± 2.62 (y), weight: 71.00 ± 11.68 (kg), height: 1.77 ± 0.05 (m)] and control [n = 12, age: 22.08 ± 2.21 (y), weight: 72.15 ± 13.24 (kg), height: 1.78 ± 0.06 (m)] groups. The experimental group performed a training program for eight weeks, three times per week. Moreover, the angular displacement and acceleration of head and neck in Tsuki punch during muscular fatigue were measured by motion analysis system before and after the training protocol. Data were analyzed by paired t-test, independent t-test, and analysis of covariance (ANCOVA) at the significance level of 0.05. Results: There was a significant difference in angular displacement (Experimental: 2.95 ± 1.85, Control: 4.15 ± 2.15) and acceleration before (Experimental: 16.29 ± 9.62, Control: 70.17 ± 12.23) and after (Experimental: 24.69 ± 15.98, Control: 70.86 ± 14.92) hitting the punching bag. Conclusion: The outcome of this study showed that proprioception training can improve head and neck postural stability during muscular fatigue against external perturbation in Karate athletes. Therefore, these exercises can be used to reduce the effect of external perturbation on the head and neck of these athletes.

A Proposed Algorithm to Assess Concussion Potential in Rear-End Motor Vehicle Collisions: A Meta-Analysis.

Concussions represent an increasing economic burden to society. Motor vehicle collisions (MVCs) are of the leading causes for sustaining a concussion, potentially due to high head accelerations. The change in velocity (i.e., delta-V) of a vehicle in a MVC is an established metric for impact severity. Accordingly, the purpose of this paper is to analyze findings from previous research to determine the relation between delta-V and linear head acceleration, including occupant parameters. Data was collected from previous research papers comprising both linear head acceleration and delta-V at the time of incident, head position of the occupant, awareness of the occupant prior to impact, as well as gender, age, height, and weight. Statistical analysis revealed the following significant power relation between delta-V and head acceleration: head acceleration = 0.465delta‐V1.3231 (R2 = 0.5913, p < 0.001). Further analysis revealed that alongside delta-V, the occupant's gender and head position prior to impact were significant predictors of head acceleration (p = 0.022 and p = 0.001, respectively). The strongest model developed in this paper is considered physiologically implausible as the delta-V corresponding to a theoretical concussion threshold of 80 g exceeds the delta-V associated with probability of fatality. Future research should be aimed at providing a more thorough data set of the occupant head kinematics in MVCs to help develop a stronger predictive model for the relation between delta-V and head linear and angular acceleration.

Evaluation of injury thresholds for predicting severe head injuries in vulnerable road users resulting from ground impact via detailed accident reconstructions.

The aim of this study was to evaluate the effectiveness of various head injury criteria and associated risk functions in prediction of vulnerable road users (VRUs) severe head injuries caused by ground impact during vehicle collisions. Ten VRU accidents with video information were reconstructed by using Chalmers Pedestrian Model, vehicle multi-body system models and the THUMS (Ver. 4.0.2) finite element model. The head kinematics were used to calculate injury risks for seven head kinematics-based criteria: head angular velocity and acceleration, linear acceleration, head injury criterion (HIC), head impact power (HIP) and two versions of brain injury criterion (i.e., BRIC and BrIC). In addition, the intracranial responses were used to estimate seven tissue injury criteria, Von Mises stress, shear stress, coup pressure (C.P.) and countercoup pressure (CC.P.), maximum principal strain (MPS), cumulative strain damage measure (CSDM), and dilatation damage measure (DDM). A review of the medical reports for all cases indicated that each individual suffered severe head injuries and died. The injury risks predicted through simulations were compared to the head injuries recorded in the medical or forensic reports. The results indicated that 75-100% of the reconstructed ground impact accidents injuries were correctly predicted by angular acceleration, linear acceleration, HIC, C.P., MPS and CSDM0.15. Shear stress, CC.P. and CSDM0.25 correctly predicted 50-75% of the reconstructed accidents injuries. For angular velocity, HIP, BRIC and BrIC, the injuries were correctly predicted for less than 50% of the reconstructed accidents. The Von Mises stress and DDM did not correctly predict any reconstructed accidents injuries. The results could help to understand the effectiveness of the brain injury criteria for future head injury evaluation.

Neck Muscular Load When Using a Smartphone While Sitting, Standing, and Walking

Myoelectric activity of neck extensor muscles and head kinematic variables, when using a smartphone for one-handed browsing and two-handed texting while sitting, standing, and walking, were evaluated to compare the neck muscular load during these tasks and across the posture conditions. There has been limited research on the relation between head-down postures and the muscular load on the neck of smartphone users. Twenty-one asymptomatic young users were asked to perform one-handed browsing and two-handed texting tasks in each of the posture conditions, and the myoelectric activities of the neck extensor muscles, head kinematic variables, and upper back posture were quantified. The muscle activation level when using a phone during walking was 21.2% and 41.7% higher than that of sitting and standing on average (p < .01). Head vertical and angular accelerations were also significantly greater (p < .01) for walking than for sitting and standing conditions. Between the two conducted tasks, participants flexed their heads more significantly (p < .01) with higher activation of the neck extensor muscles (p < .01) when texting as compared to when browsing. Results indicate that two-handed texting while walking would be the most physically demanding scenario for neck musculature, and it might be attributable to the dynamics of the head while walking with the head facing downwards. These findings can be used to better understand the potential relation between smartphone use and the occurrence of neck musculoskeletal problems and to inform the users of the ergonomic risks of using smartphones while walking.

Development of a conversion model between mechanical and electrical vestibular stimuli.

The vestibular end-organs encode for linear and angular head accelerations in space contributing to our internal representation of self-motion. Activation of the vestibular system with transmastoid electrical current has recently grown in popularity; however, a direct relationship between electrically evoked and mechanically evoked vestibular responses remains elusive in humans. We have developed and tested a mechanical-to-electrical vestibular stimulus conversion model incorporating physiological activation of primary vestibular afferents identified in nonhuman primates. We compared ocular torsional responses between mechanical (chair rotation) and model-derived electrical (binaural-bipolar) stimuli in separate experiments for an angular velocity step change (±10 deg/s over 1 s, ±4-mA peak amplitude; n = 10) and multisine angular velocities (±10 deg/s, 9.7 mA peak to peak, 0.05-1 Hz; n = 5), respectively. Perception of whole body rotation (n = 18) to our step-change stimuli was also evaluated. Ocular torsional slow-phase velocity responses between stimulation types were similar (paired two one-sided tests of equivalence: multiple P < 0.002; one-sample t test: P = 0.178) and correlated (Pearson's coefficient: multiple P < 0.001). Bootstrap analysis of perceived angular velocity likewise showed similarity in perceptual decay dynamics. These data suggest that central processing between stimuli was similar, and our vestibular stimulus conversion model with a conversion factor of ∼0.4 mA per deg/s for an angular velocity step change can generate electrical stimuli that replicates dynamic vestibular activation elicited by mechanical whole body rotations. This proposed vestibular conversion model represents an initial framework for using electrical stimuli to generate mechanically equivalent activation of primary vestibular afferents for use in biomedical applications and immersive reality technologies.NEW & NOTEWORTHY With the growing popularity of electrical vestibular stimulation in biomedical and immersive reality applications, a direct conversion model between electrical and mechanical vestibular stimuli is needed. We developed a model to generate electrical stimuli mimicking the physiological activation of vestibular afferents evoked by mechanical rotations. Ocular and perceptual responses evoked by mechanical and model-derived electrical stimuli were similar, thus providing a critical first step toward generation of electrically induced vestibular responses that have a realistic mechanical equivalent.

Vulnerable Locations on the Head to Brain Injury and Implications for Helmet Design.

In studying traumatic brain injury (TBI), it has been long hypothesized that the head is more vulnerable to injury from impacts in certain directions or locations, as the relationship between impact force and the resulting neurological outcome is complex and can vary significantly between individual cases. Many studies have identified head angular acceleration to be the putative cause of brain trauma, but it is not well understood how impact location can affect the resulting head kinematics and tissue strain. Here, we identify the susceptibility of the head to accelerations and brain strain from normal forces at contact points across the surface of the skull and jaw using a three-dimensional, 20-degree-of-freedom rigid-body head and cervical spine model. We find that head angular acceleration and brain tissue strain resulting from an input force can vary by orders of magnitude based on impact location on the skull, with the mandible as the most vulnerable region. Conversely, head linear acceleration is not sensitive to contact location. Using these analyses, we present an optimization scheme to distribute helmet padding thickness to minimize angular acceleration, resulting in a reduction of angular acceleration by an estimated 25% at the most vulnerable contact point compared to uniform thickness padding. This work gives intuition behind the relationship between input force and resulting brain injury risk, and presents a framework for developing and evaluating novel head protection gear.

Why the semicircular canals are not stimulated by linear accelerations

Head accelerations are sensed by the vestibular system in the inner ear. Linear accelerations stimulate the otolith organs, while the semicircular canals (SCC) sense angular accelerations. Fluid–structure interaction (FSI) models of the cupula sensor (simulated with finite element method (FEM)) and the endolymph fluid (simulated with computational fluid dynamics (CFD)) in the semicircular canal offer the possibility to investigate why the SCC are not stimulated by linear accelerations. Two hypotheses exist in the literature. The first hypothesis focusses on the density of the cupula sensor in the SCC, while the second is based on the continuous loop of fluid in the semicircular canal. However, neither increasing the cupula density, nor disrupting the continuous fluid circulation substantially increase the cupula deformation under linear head acceleration, thereby rejecting both existing hypotheses. We propose an alternative hypothesis, based on the circular geometry of the semicircular canal. During angular head acceleration, the cupula intersects the body of endolymph and ‘pushes’ it forward because the cupula seals the semicircular canal like a diaphragm. This results in cupula deflection and neural stimulation. During linear head acceleration, on the other hand, a large part of the canal wall also ‘pushes’ the endolymph forward, which leads to hardly any cupula deflection.

Role of Helmet Fit on Angular and Linear Accelerations of Head in Ice Hockey

Increasing the protection efficiency of helmets is counted as the biggest challenge in ice hockey. The main objective of this study is twofold: first to understand the effect of fitting on the protection capability of ice hockey helmets, and second to determine a possible optimal fit with respect to minimum head accelerations. A purpose-built monorail drop tower was utilized to perform front and front boss impacts at a velocity of 4.47m/s on a custom headform outfitted with a commercial helmet (CCM Resistance) with no gap (tight fit), 2mm (regular fit), and 5 mm gaps (loose fit). It was observed that while in both impacts linear accelerations were lower for the regular fit model, the loose fit model predicted the lowest angular accelerations. A loosely-fitted helmet provides non-deterministic shifting upon impact which generally leads to a wider standard deviation of linear and angular accelerations. The results indicated that in front impacts while introducing a gap reduced the risk of focal injuries, only the loose fit model suggested lower risks of concussive injuries. However, the regular and loose fit models showed better protection against focal and concussive injuries in the front boss impacts, respectively.

Semicircular canal biomechanics in health and disease.

The semicircular canals are responsible for sensing angular head motion in three-dimensional space and for providing neural inputs to the central nervous system (CNS) essential for agile mobility, stable vision, and autonomic control of the cardiovascular and other gravity-sensitive systems. Sensation relies on fluid mechanics within the labyrinth to selectively convert angular head acceleration into sensory hair bundle displacements in each of three inner ear sensory organs. Canal afferent neurons encode the direction and time course of head movements over a broad range of movement frequencies and amplitudes. Disorders altering canal mechanics result in pathological inputs to the CNS, often leading to debilitating symptoms. Vestibular disorders and conditions with mechanical substrates include benign paroxysmal positional nystagmus, direction-changing positional nystagmus, alcohol positional nystagmus, caloric nystagmus, Tullio phenomena, and others. Here, the mechanics of angular motion transduction and how it contributes to neural encoding by the semicircular canals is reviewed in both health and disease.

Dependency of Head Impact Rotation on Head-Neck Positioning and Soft Tissue Forces.

Humans are susceptible to traumatic brain injuries from rapid head rotations that shear and stretch the brain tissue. Conversely, animals such as woodpeckers intentionally undergo repetitive head impacts without apparent injury. Here, we represent the head as the end effector of a rigid linkage cervical spine model to quantify how head angular accelerations are affected by the linkage positioning (head-neck configuration) and the soft tissue properties (muscles, ligaments, tendons). We developed a two-pivot manipulator model of the human cervical spine with passive torque elements to represent soft tissue forces. Passive torque parameters were fit against five human subjects undergoing mild laboratory head impacts with tensed and relaxed neck muscle activations. With this representation, we compared the effects of the linkage configuration dependent end-effector inertial properties and the soft tissue resistive forces on head impact rotation. Small changes in cervical spine positioning (<5 degrees) can drastically affect the resulting rotational head accelerations (>100%) following an impact by altering the effective end-effector inertia. Comparatively, adjusting the soft tissue torque elements from relaxed to tensed muscle activations had a smaller (<30%) effect on maximum rotational head accelerations. Extending our analysis to a woodpecker rigid linkage model, we postulate that woodpeckers experience relatively minimal head impact rotation due to the configuration of their skeletal anatomy. Cervical spine positioning dictates the head angular acceleration following an impact, rather than the soft tissue torque elements. This analysis quantifies the importance of head positioning prior to impact, and may help us to explain why other species are naturally more resilient to head impacts than humans.