Proceedings of the Institution of Mechanical Engineers,Part P: Journal of Sports Engineering and Technology

Acute subdural hematoma is one of the most frequent head injuries observed in victims of bicycle-related accidents. For nearly one third of the acute subdural hematoma cases, the etiopathology directly relates to the rupture of a bridging vein. To gain a better insight into the biomechanical characteristics of acute subdural hematoma following a head impact, an accurate description of the bridging vein material behaviour is essential. This study focuses on describing the material failure characteristics of the bridging vein – superior sagittal sinus complex. The junction of these bridging veins to the superior sagittal sinus has been described in the literature as an area with distinct vein wall architecture, and this should be taken into account since it might play an important role in the biomechanical response of the bridging vein to a head impact. A total of 63 bridging vein units were dissected and tested under axial loading conditions at strain rates ranging from 2.7 s⁻¹ to 20.9 s⁻¹. From the obtained load and displacement data, the ultimate stress and strain, Young’s modulus and yield stress and strain were calculated. Next, a comparison is made with published bridging vein data at lower strain rates to investigate strain rate dependency. Based on the presented data, no strain rate sensitivity could be observed in the bridging vein material behaviour. However, a gender influence was seen in both the bridging vein’s geometry and failure characteristics.

The mechanical characterization of brain tissue at high loading velocities is vital for understanding and modeling traumatic brain injury. The most severe form of traumatic brain injury is diffuse axonal injury, which involves damage to individual nerve cells (neurons). Diffuse axonal injury in animals and humans occurs at strains >10% and strain rates >10 s⁻¹. The mechanical properties of brain tissues at these strains and strain rates are of particular significance, as they can be used in finite element human head models to accurately predict brain injuries under different impact conditions. Existing conventional tensile testing machines can only achieve maximum loading velocities of 500 mm/min, whereas the Kolsky bar apparatus is more suitable for strain rates >100 s⁻¹. In this study, a custom-designed high rate tension device is developed and calibrated to estimate the mechanical properties of brain tissue in tension at strain rates ≤ 90 s⁻¹, while maintaining a uniform velocity. The range of strain can also be extended to 100% depending on the thickness of a sample. The same apparatus can be used to characterize the dynamic behavior of skin and other soft biological tissues by using appropriately sized load cells with a capacity of 10 N and above.

Concussion is a prevalent injury in collision and contact sports, but the biomechanics of concussion has mainly been assessed for helmeted head impacts. Concussion and no-injury cases had previously been reconstructed using rigid body simulations from a larger video database of unhelmeted head impact cases from Australian rules football, rugby union and rugby league. The KTH finite element human head model was used to simulate the 27 concussion and 13 no-injury cases, and the maximum principle strain levels in the corpus callosum were evaluated. The rotational kinematics and strain levels were compared to critical strain tolerance curves and reconstructed pedestrian impacts from the literature. It was found that the 5% critical strain tolerance curve equated to a maximum principal strain level of approximately 0.20 and was associated with concussive impacts involving prolonged loss of consciousness. The results suggest rotational kinematics above 4500 rad/s² and 33 rad/s for peak resultant angular acceleration and maximum change in resultant angular velocity, respectively, as tentative tolerance levels for concussion involving prolonged loss of consciousness. Cases involving short duration or no loss of consciousness had similar rotational kinematics and strain levels in the corpus callosum, suggesting that these injuries are of similar severity. The findings support the hypothesis that sports concussions share some biomechanical characteristics with diffuse axonal injury.

Modern sport helmets certified to various international safety standards have virtually eliminated the incidence of cranial fracture and fatal brain injury in contact sports; however, the occurrence of diffuse brain injuries (mTBI) are still prevalent. Local contact mechanics between the colliding surface (helmet/head) need to be considered as global measures of acceleration and are insensitive to load distribution measures which are indicative of helmet performance. The purpose of this study was to demonstrate the ability to capture localized load distribution response between the helmet and headform and to examine factors that may influence these measures. Twenty-five flexible force sensors were arranged in a 5 × 5 array about three impact sites (front, side, rear) of a 575 mm EN960 headform. Test factors included helmet model (5), impact location (3) and temperature (21 °C, −25 °C) as well as repeated impacts (3). Testing procedure followed the CSA Z262.1-09 standard at the defined locations. Average error calculated during sensor calibration was 2.8 ± 1% with an R² value of 0.987 ± 0.009. As expected, peak global force correlated well to peak acceleration (R² = 0.98) but weakly corresponded to peak focal force (R² = 0.22). Furthermore, both load distribution magnitudes and patterns were found to vary substantially with mixed effects between helmet models, impact locations, and temperatures. Given these findings, this novel approach may be used to quantify local contact mechanics between the colliding surface/helmet/head.

The international market for sports equipment is enormous. One component of that market is explicitly equipment to prevent injury, and ideally all equipment should enable performance without causing injury. This paper will describe a biomechanical approach to the design of equipment to prevent sports injury. Elements in this approach include understanding and applying: injury risk management methods to set objectives; injury mechanisms; human tolerance to loads; range of sports loads (normal and abnormal); objectives of sport and sports skills; efficacy and effectiveness of current and past equipment; user expectations (usability, mass, aesthetics); standards requirements; setting performance objectives; identifying and testing materials; assessing materials and component testing; prototype testing; final product; and product evaluation and continuous control.

Traumatic and mild traumatic brain injuries are incurred as a result of the complex motions of the head after an impact. These motions can be quantified in terms of linear and rotational accelerations which cause the injurious levels of brain deformation. Currently, it is unclear what aspects of the linear and rotational acceleration loading curves influence injurious brain deformation. This research uses the University College Dublin Brain Trauma Model to analyse the loading curve shapes from a series of centric and non-centric impacts to a Hybrid III headform fitted with different hockey helmets. The results found that peak resultant linear acceleration did not always correlate with brain deformation measures. The results also indicated that, due to the complex nature of the interaction between loading curve characteristic and tissue parameters, there was no commonality in curve shape which produced large magnitudes of brain deformation. However, the discriminant function did show that angular acceleration loading curve characteristics would predict brain deformation more reliably than linear acceleration loading curves.

Computer methods can assist in understanding the behaviour of the individual components of a helmet, beyond merely the headform output as is usually done in a laboratory environment or for test-house certification purposes. This design study uses a method that we have previously used to analyse the effects of helmet liner material properties. While the helmet liner is of vital importance for energy absorption, other design modifications can also serve to improve its performance. The equestrian helmet model previously developed and analysed by the authors was used in this study. The helmet shell and geometric factors, such as a gap between the liner and shell, ventilation holes and ridges on the helmet liner were studied to observe their influence on helmet performance. By studying helmet design variations in terms of different variables other than headform linear acceleration, it is possible to determine which helmet configurations perform better, why they perform the way they do and how efficiently they perform. This can assist the product design and optimization process by suggesting models which would optimize cost, weight and helmet size.

A linear impactor system was used to apply a condensed version of the University of Ottawa Test Protocol, employing five centric and non-centric impact conditions, to a Hybrid III headform fitted with six certified ice hockey helmets. None of the helmeted conditions exceeded linear acceleration thresholds for traumatic or mild traumatic brain injury; however, five of the six helmets had angular acceleration results that were above the 80% risk of mild traumatic brain injury threshold proposed by Zhang et al. High risk of mild traumatic brain injury was associated with non-centric impact conditions and peak angular accelerations, supporting the need for improved three-dimensional helmet certification standards.

This research was undertaken to examine a new method for assessing the performance of ice hockey helmets. It has been proposed that the current centric impact standards for ice hockey helmets, measuring peak linear acceleration, have effectively eliminated traumatic head injuries in the sport, but that angular acceleration and brain tissue deformation metrics are more sensitive to the conditions associated with concussive injuries, which continue to be a common injury. Ice hockey helmets were impacted using both centric and non-centric impact protocols at 7.5 m/s using a linear impactor. Dynamic impact responses and brain tissue deformations from the helmeted centric and non-centric head form impacts were assessed with respect to proposed concussive injury thresholds from the literature. The results of the helmet impacts showed that the method used was sensitive enough to distinguish differences in performance between helmet models. The results have shown that peak linear acceleration yielded low magnitudes of response to an impact, but peak angular acceleration and brain deformation metrics consistently reported higher magnitudes, reflecting a high risk for incurring a mild traumatic brain injury.

Currently-available jockey helmets are typically assessed against performance standards which cater to equestrian helmets for all horse riding activities; however, severe impacts and head injuries in horse racing have become the focus of concern. The EN 14572 High Performance Helmets for Equestrian Activities Standard included a series of high energy impacts and other tests, such as lateral crush, that are not included in other equestrian helmet standards. Currently no helmet has been manufactured to meet this standard. This study assessed the energy attenuation performance of several materials that could be used to construct the inner liner of a jockey helmet designed to manage head acceleration to tolerable levels in high energy impacts. Among the materials assessed, it was found that dual-material samples performed better than single-material samples, with the combination of two polyurethane foams returning the lowest peak linear headform accelerations for higher drop heights. The results from this study compared well against the results of a similar study, with samples having better energy attenuation performance and smaller thicknesses. This study demonstrates the potential for new materials, and the layering of materials with different characteristics, to be considered for use in protective helmets.

The rules and regulations of Taekwondo stipulate how the sport must be played and the necessary personal protective equipment. As such, personal protective equipment performance under controlled rigid drop-tests is also outlined. Unfortunately, these impacts do not replicate human loading effectively, making conclusions about their performance unknown. However, it may be possible to use human kinematic data to improve the biofidelity of current impactors, including a current single-segment martial arts kicking robot. Five martial artists performed a series of roundhouse kicks while reflective markers on the kicking leg and pelvis were used to track hip, knee, ankle and foot positions. Using specific single-segment martial arts kicking robot robot parameters, computer simulation was used to model a single-segment martial arts kicking robot performance (1-SM) and to form a multi-segment, multi-joint model to match human kinematic data (3-SM). The 3-SM was found to produce similar kinematics to human performance while reducing the overall effective mass at impact, motor torque and stress concentration magnitudes in the leg when compared to the 1-SM. This study suggested that human performances could be used to improve current mechanical testing techniques without introducing much complexity to improve the external validity of protective equipment evaluation testing.

A via ferrata (Italian for ‘iron road’) is a climbing route with fixed iron climbing aids in steep, rocky mountain terrain. Climbers attach themselves to the climbing aids with a via ferrata set (a certain safety equipment designed for vie ferrate) and a harness. In case of a fall the via ferrata set should prevent injuries by reducing the deceleration of the falling body. Different standards exist worldwide for the deceleration and forces acting in the case of a fall; the European standard is evaluated for 80 kg heavy individuals. In this paper the acceleration and force differences for different climber weights – especially lightweight climbers – are evaluated. For this purpose four different NCAP frontal crash dummies representing humans of different weights and ages (3 y, 15 kg; 10 y, 34 kg; female adult, 48 kg; male adult, 77 kg) were dropped from a height of 5 m into different via ferrata sets. During a fall accelerations and braking forces were measured, A/D converted with a frequency of 1024 Hz and 1000 Hz, respectively and recorded on a PC. Additionally synchronous video data were recorded with two cameras (240 fps, 448 × 336 px). A total of eight via ferrata sets of two different types were evaluated: (1) modern web-based sets where a webbing is ripped apart and absorbs energy (tearing energy absorbers), and (2) cheaper rope-braking systems which absorb energy by friction (friction energy absorbers). The results show that the maximum braking forces allowed in the European standard were exceeded in several cases. Maximum braking distances were not used to full capacity in any of the trials. Thus, falls could have caused injuries especially for lightweight climbers. Hence, according to the gathered data a minimum weight limit for via ferrata sets should be established. European standards should be adopted in consideration of the presented results of this study.

In brain injury research, linear and angular resultant acceleration data have been considered important mechanisms contributing to various levels of brain injury. The development of biofidelic headforms with similar dimensions and weight to that of a real human head has allowed for researchers to repeatedly collect data related to the effects of different impacts on the human head. Currently, there are different types of headforms available for impact testing, each with varying degrees of biofidelity and repeatability. Two commonly used headforms were tested: the Hybrid III and the Hodgson–WSU (NOCSAE). The two headforms were outfitted with nine single-axis accelerometers positioned orthogonally following a 3–2–2–2 array. Both headforms show good linearity and correlate well throughout the different velocities and are, therefore, reliable tools. Significant differences are observed in peak linear and peak angular accelerations between Hybrid III and Hodgson–WSU headforms. The shapes of the loading curves are visually different and thus may have significant impact on the output from FE modelling of the brain response.

As part of a wider project investigating the biomechanics of the rugby scrum within rugby union, the focus of the present study was to design, realise and test an unobtrusive measurement system for assessing the kinematics and kinetics of rugby forwards while scrummaging on the pitch in realistic environmental conditions. Currently the study investigates one forward pack (eight players) scrummaging against an instrumented scrum machine, a training aid used widely throughout rugby. The measurement system integrates three different subsystems for: (1) measuring forces exerted by players; (2) capturing players’ movements; and, (3) triggering/synchronising all the sensors involved in (1) and (2). Applied three-dimensional forces were measured by strain gauge circuits attached to each pusher arm of the machine and then summed to produce the components of overall force. Multiple camera views allowed the recording and subsequent analysis of player movements, in the primary transverse (50 Hz and 200 Hz) and sagittal (50 Hz) planes of motion. A control system executed pre-recorded audio commands to players with consistent timings, sent trigger pulses to acquisition devices and collected analogue data at 500 Hz. The overall system has been applied successfully in the field to record data from rugby union forward packs across a range of playing levels and initial results confirm that the measurement system will be useful for its desired purpose to compare the biomechanics of different scrum engagement techniques.

Pedal and motorcycle helmets offer a high level of protection to the wearer’s head. There is a need to review and assess the performance offered by helmets, so that helmet design and test standards can be optimized. One input into this process is crash reconstruction. Helmeted crash cases can be collected and examined, leading to insights into impact severity, helmet performance and injury outcomes. However, it is unclear to what extent residual helmet damage reflects the impact characteristics. This paper addresses this issue using controlled laboratory impact tests.

Two pedal cycle and three motorcycle helmet models were tested with an ‘M’ size headform in impact energy attenuation tests from 1 m, 2 m and 2.5 m. Headform acceleration, impact force and post-impact deformation were measured. The dynamic deformations were measured with three methods: video, kinetic energy and an analytical approach using impact force and liner yield stress.

All five models offered highly repeatable performance in terms of impact energy attenuation and acceleration management in radial impacts across the impact severities. The results showed that the Standards Australia certified helmets provided impact protection to the head in impacts that greatly exceeded the impact energy attenuation performance requirements of those standards.

The residual and dynamic deformation measurements were correlated with drop height and headform acceleration for pedal cycle helmets. The results indicate that the residual deformation observed in a pedal cycle helmet collected from a crash can be used to estimate the impact severity and, after undertaking exemplar impact tests on the same model helmet, the head impact acceleration. However, the residual deformation measured on the three motorcycle helmets was not correlated with the drop height, which indicated that, within the limits of this study, estimating crash severity from motorcycle helmet damage is not reliable.

In 2009 approximately half of the French population owned a bicycle. However, the cyclist’s accident rate is the highest of all road users. Hence, it is necessary to set up a protection system for cyclists, especially for the cephalic segment. Currently, relatively little literature has dealt with the head impact condition for this kind of accident, especially for cases of cyclist falls. Therefore, the objective of this work was to identify the initial conditions for head impact in cases of cycling fall accidents. The present paper proposes a parametric study by simulating a lot of accident scenarios. A total of 1024 simulations have been automatically carried out using Madymo^®’s software and a specially designed program. Two situations of cycling falls have been investigated according to real accident configuration: cyclist falls due to skidding and after hitting a curb. The TNO (Dutch Organization for Applied Scientific Research, Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek) pedestrian 50th percentile human model was coupled to a city bicycle model. The analysed outputs are head impact area and head velocity before impact. The work has provided a solid information base for future work on cyclist accidents. The parametric analysis was also used to study the effects of poorly known environmental parameters, such as speed or torso inclination. The results provided estimates of the impact area and speed of the head, which helps to improve the design of safer helmets and of helmet certification standards tests.

Traumatic brain injuries contribute to a high degree of morbidity and mortality in society. To study traumatic brain injuries researchers reconstruct the event using both physical and FE models. The purpose of these reconstructions is to correlate the brain deformation metric to the type of injury as a measure for prediction. These reconstructions are guided by a series of independent variables which all have influence upon the outcome variables. This research uses a combination of physical and FE modelling to quantify how independent variables such as velocity and impact vector (angle) contribute to the resulting variance in brain deformation metrics. The results indicated that using a Hybrid III neck controls the rotational acceleration response from an impact. Also, it was found that strain rate and product of strain and strain rate were more sensitive to changes in impact angle. Linear acceleration decreased with increasing impact angle, while brain deformations did not follow this trend, which suggests that peak linear acceleration may not be the only factor in the production of larger brain deformations.