Gary T. Yamaguchi

Electromyographic activity and posturing of the human neck during rollover tests

Lateral head motions, torso motions, lateral neck bending angles, and electromyographic (EMG) activity patterns of five human volunteer passengers are compared to lateral motions of a Hybrid III ATD during right-left and left-right fishhook steering maneuvers leading to vehicular tip-up. While the ATD maintained relatively fixed lateral neck angles, live subjects leaned their heads slightly inward and actively utilized their neck musculature to stiffen their necks against the lateral inertial loads. Except for differences in neck lateral bending, the Hybrid III ATD reasonably reflects occupant kinematics during the pre-trip phase of on-road rollovers.

Joint-specific changes in locomotor complexity in the absence of muscle atrophy following incomplete spinal cord injury.

BackgroundFollowing incomplete spinal cord injury (iSCI), descending drive is impaired, possibly leading to a decrease in the complexity of gait. To test the hypothesis that iSCI impairs gait coordination and decreases locomotor complexity, we collected 3D joint angle kinematics and muscle parameters of rats with a sham or an incomplete spinal cord injury.Methods12 adult, female, Long-Evans rats, 6 sham and 6 mild-moderate T8 iSCI, were tested 4 weeks following injury. The Basso Beattie Bresnahan locomotor score was used to verify injury severity. Animals had reflective markers placed on the bony prominences of their limb joints and were filmed in 3D while walking on a treadmill. Joint angles and segment motion were analyzed quantitatively, and complexity of joint angle trajectory and overall gait were calculated using permutation entropy and principal component analysis, respectively. Following treadmill testing, the animals were euthanized and hindlimb muscles removed. Excised muscles were tested for mass, density, fiber length, pennation angle, and relaxed sarcomere length.ResultsMuscle parameters were similar between groups with no evidence of muscle atrophy. The animals showed overextension of the ankle, which was compensated for by a decreased range of motion at the knee. Left-right coordination was altered, leading to left and right knee movements that are entirely out of phase, with one joint moving while the other is stationary. Movement patterns remained symmetric. Permutation entropy measures indicated changes in complexity on a joint specific basis, with the largest changes at the ankle. No significant difference was seen using principal component analysis. Rats were able to achieve stable weight bearing locomotion at reasonable speeds on the treadmill despite these deficiencies.ConclusionsDecrease in supraspinal control following iSCI causes a loss of complexity of ankle kinematics. This loss can be entirely due to loss of supraspinal control in the absence of muscle atrophy and may be quantified using permutation entropy. Joint-specific differences in kinematic complexity may be attributed to different sources of motor control. This work indicates the importance of the ankle for rehabilitation interventions following spinal cord injury.

Development of a computational method to predict occupant motions and neck loads during rollovers

The mechanics of on-road, friction-induced rollovers were studied with the aid of a three-dimensional computer code specifically derived for this purpose. Motions of the wheels, vehicle body, occupant torso, and head were computed. Kanes method was utilized to develop the dynamic equations of motion in closed form. On-road rollover kinematics were compared to a dolly-type rollover at lesser initial speed, but generating a similar roll rotation rate. The simulated on-road rollover created a roof impact on the leading (drivers) side, while the dolly rollover simulation created a trailing-side roof impact. No head-to-roof contacts were predicted in either simulation. The first roof contact during the dolly-type roll generated greater neck loads in lateral bending than the on-road rollover. This work is considered to be the first step in developing a combined vehicle and occupant computational model for studying injury potential during rollovers.

Conducting high frequency electrical measurements — Case study using a TASER M18 device

A number of measuring instruments are currently available for conducting dc and low frequency electrical measurements. However, to achieve a high degree of accuracy in high-voltage, high-frequency measurements for pulse power applications at low repetition rates requires careful adherence to established electrical procedures. Measurement errors may be introduced due to a variety of reasons. Parasitic elements may also play a significant role. The authors conducted a series of electrical tests to determine the output current waveforms and the power dissipated for a device operating at a high voltage and high frequency with a low duty cycle. The device of choice was a new TASER® M18, used in the “drive-stun” mode and connected to eleven load resistances. Output current waveforms were recorded. The power dissipated in the various load resistances was also computed. The authors further compare their results with a series of measurements reported in the article, “Forensic Engineering Analysis of Electro-Shock Weapon Safety,” by James A. Ruggieri, P.E. This article was published by the Journal of the National Academy of Forensic Engineers, Vol. XXII, No. 2, December 2005, p. 19–48. In this article, Mr. Ruggieri reported his measurements of the electrical power outputs for the M18, alleging that as the output resistance decreased, the “Power Contributing Interval” (PCI) and consequently the output power, increased substantially. This paper also presents comparisons of the waveforms generated by the authors versus those presented by Mr. Ruggieri, and graphically compares the values of the calculated output power. This paper illustrates the importance of adhering to proper measurement techniques when conducting high-voltage, high-frequency measurements.

Effects of spinal cord injury-induced changes in muscle activation on foot drag in a computational rat ankle model

Spinal cord injury (SCI) can lead to changes in muscle activation patterns and atrophy of affected muscles. Moderate levels of SCI are typically associated with foot drag during the swing phase of locomotion. Foot drag is often used to assess locomotor recovery, but the causes remain unclear. We hypothesized that foot drag results from inappropriate muscle coordination preventing flexion at the stance-to-swing transition. To test this hypothesis and to assess the relative contributions of neural and muscular changes on foot drag, we developed a two-dimensional, one degree of freedom ankle musculoskeletal model with gastrocnemius and tibialis anterior muscles. Anatomical data collected from sham-injured and incomplete SCI (iSCI) female Long-Evans rats as well as physiological data from the literature were used to implement an open-loop muscle dynamics model. Muscle insertion point motion was calculated with imposed ankle trajectories from kinematic analysis of treadmill walking in sham-injured and iSCI animals. Relative gastrocnemius deactivation and tibialis anterior activation onset times were varied within physiologically relevant ranges based on simplified locomotor electromyogram profiles. No-atrophy and moderate muscle atrophy as well as normal and injured muscle activation profiles were also simulated. Positive moments coinciding with the transition from stance to swing phase were defined as foot swing and negative moments as foot drag. Whereas decreases in activation delay caused by delayed gastrocnemius deactivation promote foot drag, all other changes associated with iSCI facilitate foot swing. Our results suggest that even small changes in the ability to precisely deactivate the gastrocnemius could result in foot drag after iSCI.

Performance of Certified Climbing Helmets During Simulated Climbing Falls

Climbing is a popular form of recreation [Gerdes, E. M., Hafner, J. W. and Aldag, J. C., “Injury Patterns and Safety Practices of Rock Climbers,” J. Trauma Inj., Infect., Crit. Care, Vol. 61, No. 6, 2006, pp. 1517–1525.]. Head injuries account for the majority of climbing fatalities; while they cannot always be prevented, wearing a certified climbing helmet can reduce head trauma. Current helmet certification procedures require impact testing only to the upper two-thirds, emphasizing protection from falling objects and resulting in helmet models that have little to no energy mitigating capabilities around their lower rim. This study presents the case for developing new helmet testing protocols emphasizing energy mitigation during climbing falls that produce head injuries 12 times more frequently than falling objects. Suspension helmets, foam helmets, and hybrid foam/suspension helmets were tested in drop and pendulum tests producing impacts to the frontal, occipital, upper parietal, and apex regions using two different headforms and a whole-body, instrumented Hybrid-III dummy. Pendulum drop tests from 1.6 m were used to create frontal and parietal impacts against a vertical steel barrier. The foam helmet delivered average values that were near the injury thresholds established for the Hybrid-III [Mertz, H. J., Irwin, A. L. and Prasad, P., “Biomechanical and Scaling Bases for Frontal and Side Impact Injury Assessment Reference Values,” Stapp Car Crash J., Vol. 47, 2003, pp. 155–188.]. All other helmet and headform combinations produced average values significantly greater than the injury thresholds. Free drops at 2.0 m from an initially upright, backward leaning orientation created occipital impacts. The dummy first struck the feet, and then rotated backward striking the back of the head, producing an impact velocity 15 % higher than that computed for a non-rotating free fall. Only the foam and magnesium headform combination delivered sub-threshold values. Average Head Injury Criterion and peak accelerations from other combinations exceeded 5000 and 500 g, respectively. Pendulum impacts to the apex following 1.0 m drops produced neck compressions, tensions, and extensions that were well beyond neck injury thresholds. These results indicate that the three certified helmets tested do not adequately protect the head during moderate height falls producing impacts to the frontal and occipital rim.