Yun-Seok Kang

Validation of a Helmet-based System to Measure Head Impact Biomechanics in Ice Hockey

PURPOSE This study aimed to quantify differences between head acceleration measured by a helmet-based accelerometer system for ice hockey and an anthropometric test device (ATD) to validate the systems use in measuring on-ice head impacts. METHODS A Hybrid III 50th percentile male ATD head and neck was fit with a helmet instrumented with the Head Impact Telemetry (HIT) System for hockey and impacted at various speeds and directions with different interfaces between the head and helmet. Error between the helmet-based and reference peak accelerations was quantified, and the influence of impact direction and helmet-head interface was evaluated. Regression equations were used to reduce error. System-reported impact direction was validated. RESULTS Nineteen percent of impacts were removed from the data set by the HIT System processing algorithm and were not eligible for analysis. Errors in peak acceleration between the system and ATD varied from 18% to 31% and from 35% to 64% for linear and rotational acceleration, respectively, but were reduced via regression equations. The relationship between HIT System and reference acceleration varied by direction (P < 0.001) and head-helmet interface (P = 0.005). Errors in impact azimuth were approximately 4%, 10%, and 31% for side, back, and oblique back impacts, respectively. CONCLUSIONS This is the first comprehensive evaluation of peak head acceleration measured by the HIT System for hockey. The HIT System processing algorithm removed 19% of the impacts from the data set, the correlation between HIT System and reference peak resultant acceleration was strong and varied by head surface and impact direction, and the system error was larger than reported for the 6-degree-of-freedom HIT System for football but could be reduced via calibration factors. These findings must be considered when interpreting on-ice data.

Measurement of Six Degrees of Freedom Head Kinematics in Impact Conditions Employing Six Accelerometers and Three Angular Rate Sensors (6aω Configuration)

The ability to measure six degrees of freedom (6 DOF) head kinematics in motor vehicle crash conditions is important for assessing head-neck loads as well as brain injuries. A method for obtaining accurate 6 DOF head kinematics in short duration impact conditions is proposed and validated in this study. The proposed methodology utilizes six accelerometers and three angular rate sensors (6aω configuration) such that an algebraic equation is used to determine angular acceleration with respect to the body-fixed coordinate system, and angular velocity is measured directly rather than numerically integrating the angular acceleration. Head impact tests to validate the method were conducted using the internal nine accelerometer head of the Hybrid III dummy and the proposed 6aω scheme in both low (2.3 m/s) and high (4.0 m/s) speed impact conditions. The 6aω method was compared with a nine accelerometer array sensor package (NAP) as well as a configuration of three accelerometers and three angular rate sensors (3aω), both of which have been commonly used to measure 6 DOF kinematics of the head for assessment of brain and neck injuries. The ability of each of the three methods (6aω, 3aω, and NAP) to accurately measure 6 DOF head kinematics was quantified by calculating the normalized root mean squared deviation (NRMSD), which provides an average percent error over time. Results from the head impact tests indicate that the proposed 6aω scheme is capable of producing angular accelerations and linear accelerations transformed to a remote location that are comparable to that determined from the NAP scheme in both low and high speed impact conditions. The 3aω scheme was found to be unable to provide accurate angular accelerations or linear accelerations transformed to a remote location in the high speed head impact condition due to the required numerical differentiation. Both the 6aω and 3aω schemes were capable of measuring accurate angular displacement while the NAP instrumentation was unable to produce accurate angular displacement due to double numerical integration. The proposed 6aω scheme appears to be capable of measuring accurate 6 DOF kinematics of the head in any severity of impact conditions.

Measurement of Hybrid III Head Impact Kinematics Using an Accelerometer and Gyroscope System in Ice Hockey Helmets

Helmet-based instrumentation is used to study the biomechanics of concussion. The most extensively used systems estimate rotational acceleration from linear acceleration, but new instrumentation measures rotational velocity using gyroscopes, potentially reducing error. This study compared kinematics from an accelerometer and gyroscope-containing system to reference measures. A Hybrid III (HIII) adult male anthropometric test device head and neck was fit with two helmet brands, each instrumented with gForce Tracker (GFT) sensor systems in four locations. Helmets were impacted at various speeds and directions. Regression relationships between GFT-measured and reference peak kinematics were quantified, and influence of impact direction, sensor location, and helmet brand was evaluated. The relationship between the sensor output and the reference acceleration/velocity experienced by the head was strong. Coefficients of determination for data stratified by individual impact directions ranged from 0.77 to 0.99 for peak linear acceleration and from 0.78 to 1.0 for peak rotational velocity. For the data from all impact directions combined, coefficients of determination ranged from 0.60 to 0.80 for peak resultant linear acceleration and 0.83 to 0.91 for peak resultant rotational velocity. As expected, raw peak resultant linear acceleration measures exhibited large percent differences from reference measures. Adjustment using regressions resulted in average absolute errors of 10–15% if regression adjustments were done by impact direction or 25–40% if regressions incorporating data from all impact directions were used. Average absolute percent differences in raw peak resultant rotational velocity were much lower, around 10–15%. It is important to define system accuracy for a particular helmet brand, sensor location, and impact direction in order to interpret real-world data.

The effect of age on the structural properties of human ribs

Traumatic injury from motor vehicle crashes is a major cause of morbidity and mortality in the United States. The thorax is particularly at risk in motor vehicle crashes and is studied extensively by the injury biomechanics community. Unfortunately, most samples used in such research generally do not include children or the very elderly, despite the common occurrence of thorax injuries at both ends of the age spectrum. Rib fractures in particular, are one of the most common injuries, especially in the elderly, and can greatly affect morbidity, mortality, and quality of life. As the proportion of older adults in the population increases, such age-related fragility fractures will continually grow as a worldwide problem. Additionally, the risk of rib fracture significantly increases with age with confounding deleterious effects. Studies on elderly ribs are not uncommon, however very few studies exist which explore the mechanical properties and behavior of immature human bone, especially of ribs. Previous research identifying rib properties has provided useful information for numerous applications. However, no study has included a comprehensive sample of all ages (pediatric through elderly) in which ribs are tested in the same repeatable set-up. The goal of this study is to characterize differences in rib structural response across the age spectrum. One-hundred forty excised ribs from 70 individuals were experimentally tested in a custom-built pendulum fixture simulating a dynamic frontal impact. The sample includes individuals of ages ranging from six to 99 years old and includes 58 males and 12 females. Reported data include fracture location, displacement in the X and Y directions at fracture (δX, δY), force at fracture (FX), and linear structural stiffness (K). δX and K exhibit a statistically significant linear decrease with age (p<0.0001). FX reveals a trend in which a peak is reached in the young adult years (25-40). Detailed mechanical property data, as provided here, will prove useful for application in computational modeling efforts, which are vital to help prevent injury and to understand injury mechanisms from childhood through old age.

AGE AND SEX ALONE ARE INSUFFICIENT TO PREDICT HUMAN RIB STRUCTURAL RESPONSE TO DYNAMIC A-P LOADING

Thoracic injuries from motor vehicle crashes (MVCs) are common in children and the elderly and are associated with a high rate of mortality for both groups. Rib fractures, in particular, are linked to high mortality rates which increase with the number of fractures sustained. Anthropomorphic test devices (ATDs) and computational models have been developed to improve vehicle safety, however these tools are constructed based on limited physical datasets. To-date, no study has explored variation of rib structural properties across the entire age spectrum with data obtained using the same experimental methodology to allow for comparison. One-hundred eighty-four ribs from 93 post mortem human subjects (PMHS) (70 male, 23 female; ages 4-99) were subjected to dynamic bending tests simulating a frontal impact to the thorax. Structural mechanical properties were calculated and a multi-level statistical model quantified the sample variance as explained by age and sex. Displacement (δX), peak force (Fpeak), linear structural stiffness (K), energy absorption to fracture (Utot), and plastic properties including post-yield energy absorption (UPl), plastic displacement (δPl), and the ratio of elastic to secant stiffness (K-ratio) all showed negative relationships with age, while only Fpeak, K, and Utot were dependent on sex. Despite these relationships being statistically significant, only 7-39% of variance is explained by age and only 3-17% of variance is explained by sex. This demonstrates that variability in bone properties is more complex than simply chronological age- and sex-dependence and should be explored in the context of biological mechanisms instead.

Comparison of Cervical Vertebrae Rotations for PMHS and BioRID II in Rear Impacts

Objective: The objectives of this study are to propose a new instrumentation technique for measuring cervical spine kinematics, validate it, and apply the instrumentation technique to postmortem human subjects (PMHS) in rear impact sled tests so that cervical motions can be investigated. Methods: First, a new instrumentation and dissection technique is proposed in which instrumentation (3 accelerometers, 3 angular rate sensors) capable of measuring the detailed intervertebral kinematics are installed on the anterior aspects of each vertebral body with minimal muscular damage. The instrumentation was validated by conducting 10 km/h rear impact tests with 2 PMHS in a rigid rolling chair. After this validation, a total of 14 sled tests using 8 male PMHS (175 ± 6.9 cm stature and 78.4 ± 7.7 kg weight) were conducted in 2 moderate-speed rear impacts (8.5 g, 17 km/h; 10.5 g, 24 km/h). A current rear impact dummy, BioRID II, was also tested under the same condition with an angular rate sensor installed on each of the cervical vertebrae so that rotations of the cervical spine of the BioRID II could be compared to those measured from the PMHS. The National Highway Traffic Safety Administration (NHTSA) biofidelity ranking system was used for quantitative analysis of the BioRID II cervical spine biofidelity. Results: Results show that the BioRID II exhibited comparable rotations to the PMHS in the 17 km/h test, but the vertebrae in the lower cervical spine (C5–C7) of the BioRID II showed less rearward rotation than the PMHS. For the 24 km/h test, the vertebrae in the cervical spine of the BioRID II exhibited less rearward rotation than the PMHS at all levels (C2–C7). The average biofidelity score for C2 through C7 was 1.02 for the 17 km/h test, and 2.27 for the 24 km/h test. Conclusions: These results reflect the fact that the fully articulated spine of the BioRID II was designed and tuned to model low speed rear impacts. The intervertebral rotations for both the PMHS and the BioRID II were primarily relative flexion rotations even though the cervical vertebrae rotated rearward with respect to the global coordinate system. Supplemental materials are available for this article. Go to the publishers online edition of Traffic Injury Prevention to view the supplemental file.

Comparison of Q3s ATD biomechanical responses to pediatric volunteers

Objective: The biofidelity of pediatric anthropomorphic test devices (ATDs) continues to be evaluated with scaled-down adult data, a methodology that requires inaccurate assumptions about the likeness of biomechanical properties of children and adults. Recently, evaluation of pediatric ATDs by comparison of pediatric volunteer (PV) data has emerged as a valuable and practical alternative to the use of scaled adult data. This study utilized existing PV data to evaluate a 3-year-old side impact ATD, the Q3s. Though ATDs have been compared to volunteer responses in frontal impacts, this study is the first to extend ATD-PV comparison methods to the Q3s ATD and among the first to extend these methods to side impacts. Methods: Previously conducted experiments were replicated in order to make a direct comparison between the Q3s and PVs. PV data were used from 4- to 7-year-olds (shoulder tests, n = 14) and 6- to 8-year-olds (sled tests, n = 7). Force–deflection data were captured during quasistatic shoulder tests through manual displacement of the shoulder joint. Resulting shoulder stiffness was compared between the Q3s and PVs. Low-speed far-side sled tests were conducted with the Q3s at lateral (90°) and oblique (60°) impacts. Primary outcomes of interest included (1) lateral displacement of the torso, (2) torso rollout angle, and (3) kinematic trajectories of the head and neck. Results: The Q3s exhibited shoulder stiffness values at least 32 N/mm greater than the PVs for all conditions (PV muscle tensed and relaxed, deflection calculated for full- and half-thoracic). In lateral sled tests, the Q3s demonstrated increased coronal torso rollout (Q3s: 49.2°; PVs: 35.7° ± 12.4°) and lateral (ΔY) movement of the top of the head (Q3s: −389 mm; PVs: −320 ± 23 mm) compared to PVs. In oblique trials, the Q3s achieved significantly decreased lateral torso displacement (Q3s: 153.3 mm; PVs: 193.6 ± 25.6 mm) and top of the head forward (ΔX) motion (Q3s: 68 mm; PVs: 133 ± 20 mm) compared to PVs. In all tests, greater downward (ΔZ) excursions of C4 and T1 were observed in the Q3s relative to PVs. Conclusions: Increased Q3s shoulder stiffness could affect head–neck kinematics as well as thorax responses because unrealistic force can be transmitted to the spine from the shoulder. Q3s and PV trajectories were of similar shape, although Q3s head kinematics displayed rigid body motion followed by independent lateral bending of the head, suggesting cervical and thoracic spine rigidity compared to PVs.

Walking pattern generation for a biped robot using optimized polynomial approximation

A stable walking pattern generation method for a biped robot is presented in this paper. The proposed method is based on the optimized polynomial approximation of the trunk motion along the moving direction. Foot motions can be designed according to the ground condition and walking speed. The trunk motion to minimize the deviation of desired ZMP is approximated by the fifth order polynomial. Small deviation of the desired ZMP is allowed to improve the walking speed. And the optimization method is employed to guarantee walking stability. To verify the effectiveness and validity of the proposed method, walking simulations are performed for the biped robot with relatively low and high speed. A numerical results show that the proposed method can be applied to the generation of stable walking pattern effectively. Keyuor&: Optimized polynomial approximation; ZMP(zero moment point); biped robot; stable walking pattern

Walking Pattern Generation employing DAE Integration Method

A stable walking pattern generation method for a biped robot is presented in this paper In general, the ZMP (zero moment point) equations, which are expressed as differential equations, are solved to obtain a stable walking pattern However, the number of differential equations is less than that of unknown coordinates in the ZMP equations It is impossible to integrate the ZMP equations directly since one or more constraint equations are involved in the ZMP equations To overcome this difficulty, DAE (differential and algebraic equation) solution method is employed The proposed method has enough flexibility for various kinematic structures Walking simulation for a virtual biped robot is performed to demonstrate the effectiveness and validity of the proposed method The method can be applied to the biped robot for stable walking pattern generation

Top tether effectiveness during side impacts

ABSTRACT Objective: Few studies have looked at the effectiveness of the top tether during side impacts. In these studies, limited anthropomorphic test device (ATD) data were collected and/or few side impact scenarios were observed. The goal of this study was to further understand the effects of the top tether on ATD responses and child restraint system (CRS) kinematics during various side impact conditions. Methods: A series of high-speed near-side and far-side sled tests were performed using the FMVSS213 side impact sled buck and Q3s ATD. Tests were performed at both 10° and 30° impacts with respect to the pure lateral direction. Two child restraints, CRS A and CRS B, were attached to the bench using flexible lower anchors. Each test scenario was performed with the presence and absence of a top tether. Instrumentation recorded Q3s responses and CRS kinematics, and the identical test scenarios with and without a top tether attachment were compared. Results: For the far-side lateral (10°) and oblique (30°) impacts, top tether attachment increased resultant head accelerations by 8–38% and head injury criterion (HIC15) values by 20–140%. However, the top tether was effective in reducing lateral head excursion by 5–25%. For near-side impacts, the top tether resulted in less than 10% increases in both resultant head acceleration and HIC15 in the lateral impact direction. For near-side oblique impacts, the top tether increased HIC15 by 17.3% for CRS A and decreased it by 19.5% for CRS B. However, the injury values determined from both impact conditions were below current injury assessment reference values (IARVs). Additionally, the top tether proved beneficial in preventing forward and lateral CRS rotations. Conclusions: The results show that the effects of the top tether on Q3s responses were dependent on impact type, impact angle, and CRS. Tether attachments that increased head accelerations and HIC15 values were generally counterbalanced by a reduction in head excursion and CRS rotation compared to nontethered scenarios.