Impact Biomechanics Research Articles

Impact biomechanics in sports and exercise: Understanding the mechanical forces behind sports-related injuries

Impact biomechanics in sports and exercise: Understanding the mechanical forces behind sports-related injuries

Research on the centre-of-mass adjustment method for the head of an anthropometric test device based on a head impact biomechanics model

Head injury is the primary cause of serious lesions or death in automobile accidents. During crash tests, the mass and centre-of-mass position of the head of anthropometric test devices are crucial factors determining the accuracy of head injury test data. However, owing to the irregular shape as well as complex structure and material composition of the head of dummies, problems such as uneven mass distribution easily occur, resulting in deviations between the actual and designed positions of the centre-of-mass of the head. This study conducted research on head impact biomechanics and the centre-of-mass adjustment method for the head of dummies. Specifically, the biomimetic mechanical equivalent of the head was investigated, and head impact mechanics were analysed. Then, a predictive model was established for head drop mechanical response; the accuracy of this model was verified through head drop experiments. Based on the model, the law of centre-of-mass influence on the mechanical response of the dummy head was investigated, yielding an evaluation method for the different mechanical responses of the head. Using the rotational centre-of-mass measurement method, the mass and centre-of-mass position of the head were obtained. The distributed centre-of-mass adjustment method based on the principle of torque equilibrium was utilized to solve the deviations in the centre-of-mass position, the geometric dimensions of the counterweights and the centre-of-mass itself. Two counterweights were distributed on both sides of the internal cavity wall of the dummy head, resolving the positioning issue of the counterweights in the head cavity. The rationality of the centre-of-mass adjustment results was analysed using the predictive model for head impact mechanical response. The analysis results indicate that the centre-of-mass-adjusted dummy head better aligned with the mechanical response of the head in real collision scenarios, providing a new approach for the adjustment of the centre-of-mass of the head of dummies.

Skeletal muscle extracellular matrix structure under applied deformation observed using second harmonic generation microscopy

The mechanical and structural properties of passive skeletal muscle are important for musculoskeletal models in impact biomechanics, rehabilitation engineering and surgical simulation. Passive properties of skeletal muscle depend strongly on the architecture of the extracellular matrix (ECM), but the structure of ECM and its realignment under applied deformation remain poorly understood. We apply second harmonic generation (SHG) microscopy to study muscle ECM in intact muscle samples both under deformation and in the undeformed state. A method for regional relocation was developed, so that the same ECM segment could be viewed before and after applying deformations. Skeletal muscle ECM was viewed at multiple scales and in three states: undeformed, under compression and under tension. Results show that second harmonic generation microscopy provides substantial detail of skeletal muscle ECM over a wide range of length scales, especially the perimysium structure. We present images of individual portions of skeletal muscle ECM both undeformed and subjected to tensile/compressive deformation. We also present data showing the response of the perimysium to a partial thickness cut applied to a section under tensile deformation. Statement of significanceSecond Harmonic Generation (SHG) microscopy is an imaging technique which takes advantage of a non-linear and coherent frequency doubling optical effect that is present in a small number of biological molecules, primarily collagen Type I, II and myosin. Collagen I is the most abundant collagen type in skeletal muscle, making SHG a promising option for visualisation of the skeletal muscle extracellular matrix (ECM). SHG microscopy does not require fixing or staining. This short communication presents the application of SHG microscopy to skeletal muscle ECM to improve our understanding of how collagen fibres reorganise under applied tensile and compression, including microscopic observations of collagen fibre reorganisation for intact samples by using a method to re-identify specific regions in repeated deformation tests.

Women in impact biomechanics research

Women in impact biomechanics research

Thoughts and perspectives on biomechanical numerical models under impacts: Are women forgotten from research?

The present paper explores a series of articles in the literature which deal with impact biomechanics of the head and thorax/abdomen segments, investigating the "sex specific properties/data" used in the studies. Statements in these studies are analyzed and point out, the use of male or female subjects for the developments of finite element models and their validation against experimental data. The present analysis raises the question about "androcentrism," and how biomechanical engineering findings and the design of the derived protecting devices are focused on male subjects.

Effects of a Subanesthetic Ketamine Infusion on Inflammatory and Behavioral Outcomes after Closed Head Injury in Rats.

Traumatic brain injury (TBI) affects millions of people annually, and most cases are classified as mild TBI (mTBI). Ketamine is a potent trauma analgesic and anesthetic with anti-inflammatory properties. However, ketamine's effects on post-mTBI outcomes are not well characterized. For the current study, we used the Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA), which replicates the biomechanics of a closed-head impact with resulting free head movement. Adult male Sprague-Dawley rats sustained a single-session, repeated-impacts CHIMERA injury. An hour after the injury, rats received an intravenous ketamine infusion (0, 10, or 20 mg/kg, 2 h period), during which locomotor activity was monitored. Catheter blood samples were collected at 1, 3, 5, and 24 h after the CHIMERA injury for plasma cytokine assays. Behavioral assays were conducted on post-injury days (PID) 1 to 4 and included rotarod, locomotor activity, acoustic startle reflex (ASR), and pre-pulse inhibition (PPI). Brain tissue samples were collected at PID 4 and processed for GFAP (astrocytes), Iba-1 (microglia), and silver staining (axonal injury). Ketamine dose-dependently altered locomotor activity during the infusion and reduced KC/GRO, TNF-α, and IL-1β levels after the infusion. CHIMERA produced a delayed deficit in rotarod performance (PID 3) and significant axonal damage in the optic tract (PID 4), without significant changes in other behavioral or histological measures. Notably, subanesthetic doses of intravenous ketamine infusion after mTBI did not produce adverse effects on behavioral outcomes in PID 1-4 or neuroinflammation on PID 4. A further study is warranted to thoroughly investigate beneficial effects of IV ketamine on mTBI given multi-modal properties of ketamine in traumatic injury and stress.

Progress on the impact of adjacent vertebral arch after single open door laminoplasty

Single-door laminoplasty has been widely used in the treatment of multisegment cervical myelopathy, with the clinical advantages of decompression of the spinal cord, relieving preoperative neurological symptoms or signs, and maintaining cervical mobility. However, in clinical work, patients with limited cervical spine activity after single open door laminoplasty are often encountered, and the direct contact with the adjacent vertebral arch can be observed in the postoperative X-ray of the anterior and lateral cervical spine, which is called the adjacent vertebral arch bone impact, which is one of the important causes of the limited cervical spine movement. In recent years, there have been many reports on the prevention of bone impact, although the short-term clinical effect is significant, but long-term clinical efficacy to be further study, and the cause and the pathogenesis of bone impact is no consensus, this paper on the surgery of adjacent vertebral arch impact epidemiology, biomechanics, clinical performance, surgical effect and improvement.

Modelling and characterisation of the dynamic behaviours of silicone-based composite skin simulant with short polyethylene fibres and bioactive glass particles

The field of medical injury prediction and impact biomechanics in relation to skin and its simulant materials has traditionally focused on quasi-static properties while overlooking the time-dependent behaviour strain rate sensitivity due to the challenges associated with dynamic events. In the present study, silicone-based composites reinforced with short polyethylene fibres and bioglass particles, previously identified as promising bio-integrative skin simulants, were characterised under the intermediate and high strain rates for short durations and viscoelastic behaviours for extended durations. The integration of reinforcements led to an enhancement in the compressive modulus, which elevated as the strain rate increased. Specifically, the composite with 3% reinforcement subjected to high strain rate loading exhibited a compressive modulus up to 9 times greater than that of the same material under quasi-static loading. It was found that the composites with 3% reinforcement exhibited similar dynamic behaviours to those measured in human and animal skins. Furthermore, the finite element modelling of a representative volume element of the developed composite was conducted to explore the necessity of incorporating blood vessels and pressure in numerical modelling. The results indicated that the influence of blood vessels on the viscoelastic responses of the skin simulant was more significant at high oscillated frequencies. However, the impact of blood vessels was relatively small, as evidenced by less than a 15% difference in response between models with and without blood channels under both quasi-static and harmonic loadings. Systematically characterised for the first time in both experiment and modelling, these composite skin simulants successfully emulated the dynamic properties of the human skin, offering a wide range of potential applications.

Cranial Bone Changes Induced by Mild Traumatic Brain Injuries: A Neglected Player in Concussion Outcomes?

Mild traumatic brain injuries (TBIs), particularly when repetitive in nature, are increasingly recognized to have a range of significant negative implications for brain health. Much of the ongoing research in the field is focused on the neurological consequences of these injuries and the relationship between TBIs and long-term neurodegenerative conditions such as chronic traumatic encephalopathy and Alzheimer's disease. However, our understanding of the complex relationship between applied mechanical force at impact, brain pathophysiology, and neurological function remains incomplete. Past research has shown that mild TBIs, even below the threshold that results in cranial fracture, induce changes in cranial bone structure and morphology. These structural and physiological changes likely have implications for the transmission of mechanical force into the underlying brain parenchyma. Here, we review this evidence in the context of the current understanding of bone mechanosensitivity and the consequences of TBIs or concussions. We postulate that heterogeneity of the calvarium, including differing bone thickness attributable to past impacts, age, or individual variability, may be a modulator of outcomes after subsequent TBIs. We advocate for greater consideration of cranial responses to TBI in both experimental and computer modeling of impact biomechanics, and raise the hypothesis that calvarial bone thickness represents a novel biomarker of brain injury vulnerability post-TBI.

Head-ground impact conditions and helmet performance in E-scooter falls

ObjectiveHead injuries are common injuries in E-scooter accidents which have dramatically increased in recent years. The head impact conditions and helmet performance during E-scooter accidents are barely investigated. This study aims to characterize the head-ground impact biomechanics and evaluate bicycle helmet protection in typical E-scooter falls. MethodThe finite element (FE) model of a hybrid III dummy riding an E-scooter was developed and validated. The FE model with and without a bicycle helmet was used to reproduce twenty-seven E-scooter falls caused by the collision with a curb, in which different riding speeds (10, 20, and 30 km/h), curb orientations (30, 60, and 90°), and E-scooter orientations (−15, 0, and 15°) were simulated. Head-ground impact velocities and locations were evaluated for the unhelmeted configurations while the helmet performance was evaluated with the reduction of head injury metrics. ResultsE-scooter falls always resulted in an oblique head-ground impact, with 78 % on the forehead. The mean vertical and tangential head-ground impact velocities were respectively 5.7 ± 1.5 m/s and 3.7 ± 2.0 m/s. The helmet significantly (p < 0.1) reduced the head linear acceleration, angular velocity, HIC_36, and BrIC, but not the angular acceleration. However, even with the helmet, the head injury metrics were mostly above the thresholds of severe head injuries. ConclusionTypical E-scooter falls might cause severe head injuries. The bicycle helmet was efficient to reduce head injury metrics but not to prevent severe head injuries. Future helmet standard evaluations should involve higher impact energy and the angular acceleration assessment in oblique impacts.

Differences in head impact biomechanics between playing positions in Canadian high school football players

ABSTRACT The objective of this study was to compare head impact magnitudes and time between impacts among positions in Canadian high-school football. Thirty nine players from two high-school football teams were recruited and assigned a position profile: Profile 1 (quarterback, receiver, defensive back, kicker), Profile 2 (linebacker, running back), and Profile 3 (linemen). Players wore instrumented mouthguards to measure peak magnitudes of linear and angular acceleration and velocity for each head impact throughout the season. A principal component analysis reduced the dimensionality of biomechanical variables, resulting in one principal component (PC1) score assigned to every impact. Time between impacts was calculated by subtracting the timestamps of subsequent head impacts within a session. Significant differences in PC1 scores and time between impacts occurred between playing position profiles (ps<0.001). Post-hoc comparisons determined that PC1 was greatest in Profile 2, followed by Profiles 1 and 3. Time between impacts was lowest in Profile 3, followed by Profiles 2 and 1. This study delivers a new method of reducing the multidimensionality of head impact magnitudes and suggests different Canadian high-school football playing positions experience different head impact magnitudes and frequencies, which is important for monitoring concussion and repetitive head impact exposure.

Association Between Head Impact Biomechanics and Physical Load in College Football.

Head impacts and physical exertion are ubiquitous in American football, but the relationship between these factors is poorly understood across a competitive season or even within an individual session. Gameplay characteristics, including player position and session type, may contribute to these relationships but have not been prospectively examined. The current study aimed to determine if an association exists between head impact biomechanics and physical load metrics. We prospectively studied college football players during the 2017–2021 football seasons across representative playing positions (15 offensive and defensive linemen, 11 linebackers and tight ends, and 15 defensive backs, running backs, and receivers). Participants wore halters embedded with Catapult Vector GPS monitoring systems to quantify player load and participant helmets were equipped with the Head Impact Telemetry System to quantify head impact biomechanics and repetitive head impact exposure (RHIE). Generalized linear models and linear regression models were employed to analyze in-session and season-long outcomes, while addressing factors such as player position and session type on our data. Player load was associated with RHIE (p < 0.001). Season-long player load predicted season-long RHIE (R2 = 0.31; p < 0.001). Position group affected in-session player load (p = 0.025). Both player load and RHIE were greater in games than in practices (p < 0.001), and position group did not affect RHIE (p = 0.343). Physical load burden was associated with RHIE within sessions and across an entire season. Session type affected both RHIE and player load, while position group only affected player load. Our data point to tracking physical load burden as a potential proxy for monitoring anticipated RHIE during the season.

The Effect of Soccer and Lacrosse Participation and Video Verified Head Impact Biomechanics on Clinical Concussion Measures

Neurocognitive changes have been found in participants of contact sports without documented concussions, raising concerns regarding the long-term consequences of subconcussive head impacts in sport. However, sex comparisons of neurocognitive change without reported concussions have not been completed for soccer or lacrosse athletes. Our purpose was to determine changes in clinical measures of cognitive function in uninjured collegiate lacrosse and soccer players. Men’s soccer (N=23), women’s soccer (N=36), men’s lacrosse (N=28) and women’s lacrosse (N=31) players wore xPatch head impact monitoring sensors for all practices and games. Sensors measured peak linear accelerations and peak rotational accelerations, allowing for daily density calculations. Participants completed the Sport Concussion Assessment Tool 3 and Immediate Post-Concussion and Cognitive Testing at the beginning and end of the season. For women, multiple statistically significant relationships were identified [decreased reaction time with increased cumulative peak linear acceleration (rs=-0.30, P=0.03), peak linear acceleration daily density (rs=-0.31, P=0.04), and peak rotational acceleration daily density (rs=-0.31, P=0.03) and also Immediate Post-Concussion and Cognitive Testing symptom change increased with increased cumulative peak linear acceleration (rs=-0.38, P=0.008) and cumulative peak rotational acceleration (rs=-0.37, P=0.009)]. For men, cognitive change scores, specifically concentration, had the only statistically significant relationship with cumulative peak rotational acceleration (rs=0.32, P=0.02). Men had a greater number of changes over the course of the season compared to women; however, the changes did not appear related to head impact biomechanics. Women had many statistically significant correlations between head impacts and deterioration in some constructs, especially symptoms.

Quantifying Head Impact Exposure, Mechanisms and Kinematics Using an Instrumented Mouthguard in Female High School Lacrosse

Background:There is growing concern for the neurological effects of repetitive head impacts in sports, and girls’ lacrosse represents a popular but understudied sport regarding head impact exposure. Current debate exists over the need for enhanced protective equipment, and it is important to quantify head impact exposure and biomechanics to inform policy discussions and rule changes for improved protection.Purpose:To quantify the head impact biomechanics, by impact mechanism and direction, of female high school lacrosse players during games using an instrumented mouthguard.Methods:A female high school varsity lacrosse team wore the Stanford Instrumented Mouthguard during competitive games for the 2019 season. Video footage was reviewed to confirm head impact events and remove false-positive recordings. For each impact event, the mechanism was coded as stick contact, player contact, fall, or ball contact, and the site was coded as face/jaw, forehead, crown, side, rear or indirect (i.e. body impact with no head contact). Head impact rates were calculated per athlete exposure (AE, defined as a single player participating in a game).Results:Sensor data were recorded for 15 players for 14 games and 97 AEs. During games, 31 sensor-recorded head impacts were video-confirmed resulting in a pooled average head impact rate of 0.32 impacts/AE. The 31 video-confirmed impacts were distributed among stick contacts (17, 54.8%), player contacts (12, 38.7%), and falls (2, 6.5%). There were no ball impacts. The associated peak kinematics are presented in Figure 1.1. The most common impact site was the side (11, 35.5%), followed by face/jaw (8, 25.8%), forehead (2, 6.5%), and crown (2, 6.5%). There were no impacts to the rear of the head and 8 (25.8%) impacts were indirect. The associated peak kinematics are presented in Figure 1.2.Conclusion:Stick impacts were the most common impact mechanism and resulted in the highest peak linear and angular kinematics, which may help explain why they are the most common cause of head injury in female lacrosse. By quantifying the head impact exposure, kinematics and mechanisms in female high school lacrosse, targeted injury preventions can be developed, such as rule changes and protective equipment.Figure 1.1.Peak linear acceleration (left) and peak angular velocity (right) presented for all impacts and then stratified by impact mechanism.Figure 1.2.Peak linear acceleration (left) and peak angular velocity (right) stratified by impact site. *Peak kinematics for impacts to the face/jaw were significantly higher than all other impact sites (p<0.05).

Correlation between kinematics and biomechanics of helmeted head under different impact conditions

Helmet is the most common and effective means to avoid severe injuries of human head in accidents. Nonetheless, the helmet may not completely protect the head and head injuries can still happen under impacts. To improve the protectability of helmets, this study aims to systematically investigate the impact characteristics (e.g., helmet structural behaviours, head kinematics and biomechanical responses) of a helmeted head under different impact conditions (e.g., anvil shape, impact site, impact velocity and impact angle). The helmeted head model was developed by a representative motorcycle helmet model coupled with a human head FE model, then validated through four helmet experiments under standard drop impact tests. Based upon the validated models, virtual drop impacts were performed on the helmeted head models to explore the helmet impact characteristics and head responses. A parametric study was carried out to investigate the effects of impact conditions on helmeted head responses; correlation analysis was also conducted to understand the relationships between head kinematics and biomechanical responses. It is shown that the impact conditions can significantly influence the helmet protectability and head responses; and the protectability of helmet can be improved by prolonging the compression stage to weaken head impact responses. According to the strong linear relationships between head kinematics and biomechanical responses established, three correlation equations were proposed to predict the head biomechanical responses through the given impact kinematics. This study is anticipated to advance the knowledge on the helmeted head responses under different impact conditions, thereby gaining new insight into the correlation between head impact kinematics and biomechanics, thereby providing technical guidance to the design for helmet protection.

Head Impact Exposure and Biomechanics in University Varsity Women's Soccer.

Soccer is a unique sport where players purposefully and voluntarily use their unprotected heads to manipulate the direction of the ball. There are limited soccer head impact exposure data to further study brain injury risks. The objective of the current study was to combine validated mouthpiece sensors with comprehensive video analysis methods to characterize head impact exposure and biomechanics in university varsity women’s soccer. Thirteen female soccer athletes were instrumented with mouthpiece sensors to record on-field head impacts during practices, scrimmages, and games. Multi-angle video was obtained and reviewed for all on-field activity to verify mouthpiece impacts and identify contact scenarios. We recorded 1307 video-identified intentional heading impacts and 1011 video-verified sensor impacts. On average, athletes experienced 1.83 impacts per athlete-exposure, with higher exposure in practices than games/scrimmages. Median and 95th percentile peak linear and peak angular accelerations were 10.0, 22.2 g, and 765, 2296 rad/s2, respectively. Long kicks, top of the head impacts and jumping headers resulted in the highest impact kinematics. Our results demonstrate the importance of investigating and monitoring head impact exposure during soccer practices, as well as the opportunity to limit high-kinematics impact exposure through heading technique training and reducing certain contact scenarios.

Computational prediction of head-ground impact kinematics in e-scooter falls

E-scooters are the fastest growing mode of micro-mobility with important environmental benefits. However, there are serious concerns about injuries caused by e-scooter accidents. Falls due to poor road surface conditions are a common cause of injury in e-scooter riders, and head injuries are one of the most common and concerning injuries in e-scooter falls. However, the head-ground impact biomechanics in e-scooter falls and its relationship with e-scooter speed and design, road surface conditions and wearing helmets remain poorly understood. To address some of these key questions, we predicted the head-ground impact force and velocity of e-scooter riders in different falls caused by potholes. We used multi-body dynamics approach to model a commercially available e-scooter and simulate 180 falls using human body models. We modelled different pothole sizes to test whether the pothole width and depth influences the onset of falls and head-ground impact velocity and force. We also tested whether the e-scooter travelling speed has an influence on the head-ground impact velocity and force. The simulations were carried out with three human body models to ensure that the results of the study are inclusive of a wide range of rider sizes. For our 10 in. diameter e-scooter wheels, we found a sudden increase in the occurrence of falls when the pothole depth was increased from 3 cm (no falls) to 6 cm (41 falls out of 60 cases). When the falls occurred, we found a head-ground impact force of 13.2 ± 3.4kN, which is larger than skull fracture thresholds. The head-ground impact speed was 6.3 ± 1.4 m/s, which is the same as the impact speed prescribed in bicycle helmet standards. All e-scooter falls resulted in oblique head impacts, with an impact angle of 65 ± 10° (measured from the ground). Decreasing the e-scooter speed reduced the head impact speed. For instance, reducing the e-scooter speed from 30 km/h to 20 km/h led to a 14% reduction in the mean impact speed and 12% reduction in the mean impact force, as predicted by the models. The models also showed that the median male riders were sustaining higher head-ground impact force and speed compared with the small female and large male riders. The findings of this study can assist authorities and e-scooter hiring companies to take more informed actions about road surface conditions and speed limits. These results can also help define representative impact test conditions for assessing the performance of helmets used by e-scooter riders in order to reduce head and brain injuries in e-scooter falls.

Progress Toward a Multiomic Understanding of Traumatic Brain Injury: A Review

Traumatic brain injury (TBI) is not a single disease state but describes an array of conditions associated with insult or injury to the brain. While some individuals with TBI recover within a few days or months, others present with persistent symptoms that can cause disability, neuropsychological trauma, and even death. Understanding, diagnosing, and treating TBI is extremely complex for many reasons, including the variable biomechanics of head impact, differences in severity and location of injury, and individual patient characteristics. Because of these confounding factors, the development of reliable diagnostics and targeted treatments for brain injury remains elusive. We argue that the development of effective diagnostic and therapeutic strategies for TBI requires a deep understanding of human neurophysiology at the molecular level and that the framework of multiomics may provide some effective solutions for the diagnosis and treatment of this challenging condition. To this end, we present here a comprehensive review of TBI biomarker candidates from across the multiomic disciplines and compare them with known signatures associated with other neuropsychological conditions, including Alzheimer’s disease and Parkinson’s disease. We believe that this integrated view will facilitate a deeper understanding of the pathophysiology of TBI and its potential links to other neurological diseases.

Head Impact Exposure and Mechanisms in Female High School Lacrosse via an Instrumented Mouthguard

To quantify the head impact biomechanics, by impact mechanism, of female high school lacrosse players during games using an instrumented mouthguard. There is growing concern for the neurologic effects of repetitive head impacts in sports, which have been linked with several short-term neurophysiologic deficits. Girls' lacrosse represents a popular but understudied sport with regard to head impact exposure and current debate exists as to the need for enhanced protective equipment. A female high school varsity lacrosse team wore the Stanford Instrumented Mouthguard during competitive games for the 2019 season. Video footage was reviewed to confirm head impact events and remove false-positive recordings. For each impact event, the mechanism was coded as stick contact, player contact, fall, or ball contact. Head impact rates were calculated per athlete exposure (AE, defined as a single player participating in a single game). Sensor data were recorded for 15 female varsity lacrosse players for 14 games and 97 AEs. During games, 31 sensor-recorded head impacts were video-confirmed resulting in a pooled average head impact rate of 0.32 impacts/AE. The video-confirmed impacts were distributed between stick contact (17, 54.8%), player contact (12, 38.7%), and falls (2, 6.5%). There were no ball impacts. Overall peak kinematics were 34.0 ± 26.6 g, 12.0 ± 9.1 rad/s, and 3,666.5 ± 2,987.6 rad/s2. Stick contacts had the highest peak linear acceleration (42.7 ± 32.2 g), angular velocity (14.5 ± 11.1 rad/s), and angular acceleration (4,242.4 ± 3,634.9 rad/s2). Stick impacts were the most common impact mechanism and resulted in the highest peak linear and angular kinematics, which may help explain why they are the most common cause of head injury in female lacrosse. By quantifying the head impact exposure, kinematics and mechanisms in female high school lacrosse, targeted injury preventions can be developed, such as rule changes and protective equipment.

The Influence of Headform/Helmet Friction on Head Impact Biomechanics in Oblique Impacts at Different Tangential Velocities

Oblique impacts of the helmet against the ground are the most frequent scenarios in real-world motorcycle crashes. The combination of two factors that largely affect the results of oblique impact tests are discussed in this work. This study aims to quantify the effect of the friction at the interface between the headform and the interior of a motorcycle helmet at different magnitudes of tangential velocity. The helmeted headform, with low friction and high friction surface of the headform, was dropped against three oblique anvils at different impact velocities resulting in three different magnitudes of the tangential velocity (3.27 m/s, 5.66 m/s, 8.08 m/s) with the same normal component of the impact velocity (5.66 m/s). Three impact directions (front, left-side and right-side) and three repetitions per impact condition were tested resulting in 54 impacts. Tangential velocity variation showed little effect on the linear acceleration results. On the contrary, the rotational results showed that the effect of the headform’s surface depends on the magnitude of the tangential velocity and on the impact direction. These results indicate that a combination of low friction with low tangential velocities may result into underprediction of the rotational headform variables that would not be representative of real-world conditions.