Torso Mass Research Articles

Hybrid III Manikin Lumbar Spine Loading Under Vertical Impact.

Clinical investigations have attributed lumbar spine injuries in combat to the vertical vector. Injury prevention strategies include the determination of spine biomechanics under this vector and developing/evaluating physical devices for use in live fire and evaluation-type tests to enhance Warfighter safety. While biological models have replicated theater injuries in the laboratory, matched-pair tests with physical devices are needed for standardized tests. The objective of this investigation is to determine the responses of the widely used Hybrid III lumbar spine under the vertical impact-loading vector. Our custom vertical accelerator device was used in the study. The manikin spinal column was mounted between the inferior and superior six-axis load cells, and the impact was delivered to the inferior end. The first group of tests consisted of matched-pair repeatability tests, second group consisted of adding matched-pair tests to this first group to determine the response characteristics, and the third group consisted of repeating the earlier two groups by changing the effective torso mass from 12 to 16 kg. Peak axial, shear, and resultant forces at the two ends of the spine were obtained. The first group of 12 repeatability tests showed that the mean difference in the axial force between two tests at the same velocity across the entire range of inputs was <3% at both ends. In the second group, at the inferior end, the axial and shear forces ranged from 4.9-25.2 kN to 0.7-3.0 kN. Shear forces accounted for a mean of 11 ± 6% and 12 ± 4% of axial forces at the two ends. In the third group of tests with increased torso mass, repeatability tests showed that the mean difference in the axial force between the two tests at the same velocity across the entire range of inputs was <2% at both ends. At the inferior end, the axial and shear forces ranged from 5.7-28.7 kN to 0.6-3.4 kN. Shear forces accounted for a mean of 11 ± 8% and 9 ± 3% of axial forces across all tests at the inferior and superior ends. Other data including plots of axial and shear forces at the superior and inferior ends across tested velocities of the spine are given in the paper. The Hybrid III lumbar spine when subjected to vertical impact simulating underbody blast levels showed that the impact is transmitted via the axial loading mechanism. This finding paralleled the results of axial force predominance over shear forces and axial loading injuries to human spines. Axial forces increased with increasing velocity suggesting the possibility of developing injury assessment risk curves, i.e., the manikin spine does not saturate, and its response is not a step function. It is possible to associate probability values for different force magnitudes. A similar conclusion was found to be true for both magnitudes of added effective torso mass at the superior end of the manikin spinal column. Additional matched-pair tests are needed to develop injury criteria for the Hybrid III male and female lumbar spines.

Cross-domain policy adaptation with dynamics alignment

The implementation of robotic reinforcement learning is hampered by problems such as an unspecified reward function and high training costs. Many previous works have used cross-domain policy transfer to obtain the policy of the problem domain. However, these researches require paired and aligned dynamics trajectories or other interactions with the environment. We propose a cross-domain dynamics alignment framework for the problem domain policy acquisition that can transfer the policy trained in the source domain to the problem domain. Our framework aims to learn dynamics alignment across two domains that differ in agents’ physical parameters (armature, rotation range, or torso mass) or agents’ morphologies (limbs). Most importantly, we learn dynamics alignment between two domains using unpaired and unaligned dynamics trajectories. For these two scenarios, we propose a cross-physics-domain policy adaptation algorithm (CPD) and a cross-morphology-domain policy adaptation algorithm (CMD) based on our cross-domain dynamics alignment framework. In order to improve the performance of policy in the source domain so that a better policy can be transferred to the problem domain, we propose the Boltzmann TD3 (BTD3) algorithm. We conduct diverse experiments on agent continuous control domains to demonstrate the performance of our approaches. Experimental results show that our approaches can obtain better policies and higher rewards for the agents in the problem domains even when the dataset of the problem domain is small.

Analysis of the lack of restraint with and without belt pretensioning in 40.2 km/h rear impacts

Objective In rear impacts, the seat and seatbelt are intended to provide occupant restraint and maintain the occupant on the seat with favorable kinematics and low biomechanical responses. This study analyzes the lack of restraint provided by lap-shoulder belts in rear impacts with and without pretensioning and offers thoughts on ways to provide early restraint by seatbelts. Methods Rear sled tests were conducted at 40.2 km/h (25 mph) delta V with a lap-shoulder belted, instrumented 50th Hybrid III. The dummy instrumentation included head, chest and pelvis triaxial acceleration and upper and lower neck triaxial loads and moments. Lap and shoulder belt loads were measured. High-speed video recorded different views of the occupant kinematics. In the first series, two sled tests were conducted with a Ford F-150 driver seat. One test was with the standard lap-shoulder belts only and a second with buckle pretensioner activation. In the second series, three matched tests were conducted with a Ford Escape driver seat. One test was with the lap-shoulder belts only, a second with retractor and anchor pretensioning and a third with only retractor pretensioning. The analysis included occupant kinematics, lap-belt movement and estimation of the load on the occupant’s torso. The load was the sum of force on the upper and lower torso. The upper torso mass was 30.8 kg (67.8 lb) based on GEBOD data for the 50th Hybrid III. It was multiplied by the resultant chest acceleration to calculate the upper torso force. The lower-torso mass was 30.9 kg (68.0 lb). It was multiplied by the resultant pelvic acceleration to calculate the lower torso force. The total load on the seatback was the sum of the upper and lower torso force. The change in angle (θ) of the lap belt was determined by video analysis. The angle θ was from the horizontal up to a line through the lap-belt webbing. Ways to provide early lap-belt restraint were considered. Results The rear sled testing at 40.2 km/h (25 mph) showed that the seatbelt provided essentially no restraint of the rearward movement of the occupant. The seat provided essentially all of the rearward restraint with and without pretensioning. There was minimal lap belt load in the series with the dual recliner Escape seat, except for a spike caused by pretensioning. There was more seat deformation in the tests with the single-side recliner F-150 seat. There were higher belt loads. The lap belt limited the lifting of the hips and thighs with essentially no rearward restraint of the occupant. Tension in the lap belt did not relate to restraint of rearward movement of the occupant. Seatbelts provided forward restraint of the occupant during rebound with the belts providing noticeable deceleration of the chest and pelvis. Concepts were considered to provide early lap-belt restraint. One involved a rear pretensioner that dynamically moves the lap-belt anchor forward and upward while tightening the belts in a rear impact. This provides a lap-belt angle greater than θ = 90 deg before occupant movement. With this geometry, the lap belt restrains rearward movement of the occupant and pulls the hip down early in a rear impact. Conclusion Seatbelts and pretensioners were designed for occupant restraint in frontal crashes, so it is not a surprise they do not provide much restraint of an occupant in rear impacts up to 40.2 km/h (25 mph). The lack of early lap-belt restraint is due to the unfavorable belt angle from the anchors over the hip. A concept is discussed that dynamically moves the anchors in rear impacts to provide early belt restraint.

Dynamic Modeling, Analysis, and Design Synthesis of a Reduced Complexity Quadruped with a Serpentine Robotic Tail.

Serpentine tail structures are widely observed in the animal kingdom and are thought to help animals to handle various motion tasks. Developing serpentine robotic tails and using them on legged robots has been an attractive idea for robotics. This article presents the theoretical analysis for such a robotic system that consists of a reduced complexity quadruped and a serpentine robotic tail. Dynamic model and motion controller are formulated first. Simulations are then conducted to analyze the tail's performance on the airborne righting and maneuvering tasks of the quadruped. Using the established simulation environment, systematic analyses on critical design parameters, namely, the tail mounting point, tail length, torso center of mass (COM) location, tail-torso mass ratio, and the power consumption distribution, are performed. The results show that the tail length and the mass ratio influence the maneuvering angle the most while the COM location affects the landing stability the most. Based on these design guidelines, for the current robot design, the optimal tail parameters are determined as a length of two times as long as the torso length and a weight of 0.09 times as heavy as the torso weight.

Adaptive tracking control for underactuated mechanical systems with relative degree two

The adaptive tracking state-feedback control for underactuated mechanical systems with outputs characterized by global relative degree equal to two is addressed. A new control technique called virtual control is proposed. Fictitious control inputs and outputs are introduced to achieve full actuation: the key step is to find the reference signals for the fictitious outputs so that the resulting virtual adaptive controls are zero. The adaptive control of an underactuated three-link walking robot with unknown torso mass is designed according to the proposed control strategy. Simulations show that adaptation is crucial for stable walking.

Relationships between body composition and anaerobic performance parameters in female handball players

Background and Study Aim. The purpose of this study was to investigate of the relationships between total/segmental body composition and anaerobic performance parameters in female handball players.&#x0D; Material and Methods. Voluntary 16 women handball players (age= 19.6±2.6years, body height= 168.0±5.5cm, body weight= 64.7±10.7kg), trained last 3 years, were participated to the study. Twelve of them were students from Faculty of Sports Sciences. All measurement and tests were completed in the week right after Turkish Women Handball 1th League. Total and segmental body composition parameters (body fat percentage, body fat mass, lean body mass, leg fat percentage, leg fat mass, lean leg mass, torso fat percentage, torso fat mass, and lean torso mass) of each player were evaluated with dual-energy X-ray absorptiometry method. Squat jump test for explosive power, countermovement jump test for elastic (reactive) power, and Wingate test for anaerobic power (WAnT AP) and anaerobic capacity (WAnT AC) were used. Relationships of total/segmental body composition parameters with jump and anaerobic power-capacity parameters were analysed with Pearson correlation and the probability level was set to p£0.05.&#x0D; Results. As a result of statistical analyses, there were negative relationships (p&lt;0.05) between anaerobic performance parameters (countermovement jump and anaerobic power-capacity) and total/segmental body composition parameters except for lean body mass, lean leg mass, and lean torso mass.&#x0D; Conclusions. Total/segmental body composition parameters based on endomorphy had negative effects on explosive power, elastic power, WAnT AP and WAnT AC. It is suggested that coaches should not allow female handball players to rise in ectomorphy for the anaerobic performance loss in the season finale.

Relationships between body composition and anaerobic performance parameters in female handball players

Background and Study Aim. The purpose of this study was to investigate of the relationships between total/segmental body composition and anaerobic performance parameters in female handball players.&#x0D; Material and Methods. Voluntary 16 women handball players (age= 19.6±2.6years, body height= 168.0±5.5cm, body weight= 64.7±10.7kg), trained last 3 years, were participated to the study. Twelve of them were students from Faculty of Sports Sciences. All measurement and tests were completed in the week right after Turkish Women Handball 1th League. Total and segmental body composition parameters (body fat percentage, body fat mass, lean body mass, leg fat percentage, leg fat mass, lean leg mass, torso fat percentage, torso fat mass, and lean torso mass) of each player were evaluated with dual-energy X-ray absorptiometry method. Squat jump test for explosive power, countermovement jump test for elastic (reactive) power, and Wingate test for anaerobic power (WAnT AP) and anaerobic capacity (WAnT AC) were used. Relationships of total/segmental body composition parameters with jump and anaerobic power-capacity parameters were analysed with Pearson correlation and the probability level was set to p£0.05.&#x0D; Results. As a result of statistical analyses, there were negative relationships (p&lt;0.05) between anaerobic performance parameters (countermovement jump and anaerobic power-capacity) and total/segmental body composition parameters except for lean body mass, lean leg mass, and lean torso mass.&#x0D; Conclusions. Total/segmental body composition parameters based on endomorphy had negative effects on explosive power, elastic power, WAnT AP and WAnT AC. It is suggested that coaches should not allow female handball players to rise in ectomorphy for the anaerobic performance loss in the season finale.

Boundary control for improving limiting performance in a new seatbelt model: A technique proposal

Abstract Seatbelt has been recognized as the most effective means to prevent occupant in car against being ejected out and sustaining injury caused by the impact with interior. Improving its limiting performance, such as reducing torso forward displacement and limiting force applied by seatbelt webbing, is still well worth studying. In this paper, we employ in-plane motion models that a torso impacts against the mid-span of webbing for study. On the basis of conventional seatbelt model, we put forward a new model that its two outer ends are qualified to be able to move forwards and rearwards. Studying from the standpoint of longitudinal propagations of in-webbing transverse waves, we first introduce a displacement function superposed at origin by a wave propagating inwards from boundary and a wave propagating outwards which both arrive at the origin at the same time; then analyse the properties required for a class of the functions with adjustable parameters to be competent; finally solve the inwards-propagating and the outwards-propagating waves via the function inversely, and give the corresponding boundary displacement signal that needs to be input. Theoretically, the results show that this control technique can simultaneously reduce torso maximum displacement, maximum force, rebound velocity against backrest and the duration of interaction with seatbelt webbing, especially in the case with bigger ratio of torso mass to webbing mass and smaller product of initial angle of straightened webbing, wave speed and the reciprocal of impact velocity, which is apt to cause bigger maximum forward displacement and moderate maximum force. The results also show that shortening lag time of the control input benefits the comprehensive reductions of the criteria.

Adaptive Control of Walking Robots Based on Virtual Holonomic Constraints: a Simulative Study

Abstract In this paper an adaptive scheme for the dynamic control of underactuated walking robots with impulse effects is proposed and illustrated for the case of a three-link robot with unknown torso mass. The proposed strategy is based on the virtual control technique, where fictitious control inputs and outputs are defined, which allow the design of a fully actuated-like control law; the reference signals for the virtual outputs are chosen as the solutions of a dynamic constraint, on which the fictitious controls are zero. The validity of the proposed method is motivated by Lyapunov arguments and tested by simulations.

Role of age and injury mechanism on cervical spine injury tolerance from head contact loading

ABSTRACTObjective: The objective of this study was to determine the influence of age and injury mechanism on cervical spine tolerance to injury from head contact loading using survival analysis.Methods: This study analyzed data from previously conducted experiments using post mortem human subjects (PMHS). Group A tests used the upright intact head–cervical column experimental model. The inferior end of the specimen was fixed, the head was balanced by a mechanical system, and natural lordosis was removed. Specimens were placed on a testing device via a load cell. The piston applied loading at the vertex region. Spinal injuries were identified using medical images. Group B tests used the inverted head–cervical column experimental model. In one study, head–T1 specimens were fixed distally, and C7–T1 joints were oriented anteriorly, preserving lordosis. Torso mass of 16 kg was added to the specimen. In another inverted head–cervical column study, occiput–T2 columns were obtained, an artificial head was attached, T1–T2 was fixed, C4–C5 disc was maintained horizontal in the lordosis posture, and C7–T1 was unconstrained. The specimens were attached to the drop test carriage carrying a torso mass of 15 kg. A load cell at the inferior end measured neck loads in both studies. Axial neck force and age were used as the primary response variable and covariate to derive injury probability curves using survival analysis.Results: Group A tests showed that age is a significant (P < .05) and negative covariate; that is, increasing age resulted in decreasing force for the same risk. Injuries were mainly vertebral body fractures and concentrated at one level, mid-to-lower cervical spine, and were attributed to compression-related mechanisms. However, age was not a significant covariate for the combined data from group B tests. Both group B tests produced many soft tissue injuries, at all levels, from C1 to T1. The injury mechanism was attributed to mainly extension. Multiple and noncontiguous injuries occurred. Injury probability curves, ±95% confidence intervals, and normalized confidence interval sizes representing the quality of the mean curve are given for different data sets.Conclusions: For compression-related injuries, specimen age should be used as a covariate or individual specimen data may be prescaled to derive risk curves. For distraction- or extension-related injuries, however, specimen age need not be used as a covariate in the statistical analysis. The findings from these tests and survival analysis indicate that the age factor modulates human cervical spine tolerance to impact injury.

Odontoid fracture biomechanics.

In vitro biomechanical study. To investigate mechanisms of odontoid fracture. Odontoid fractures in younger adults occur most often due to high-energy trauma including motor vehicle crashes and in older adults due to fall from standing height. Horizontally aligned head impacts into a padded barrier were simulated using a human upper cervical spine specimen (occiput through C3) mounted to a surrogate torso mass on a sled and carrying a surrogate head. We divided 13 specimens into 3 groups on the basis of head impact location: upper forehead in the midline, upper lateral side of the forehead, and upper lateral side of the head. Post-impact fluoroscopy and anatomical dissection documented the injuries. Time-history biomechanical responses were determined. Four of the 5 specimens subjected to impact to the upper forehead in the midline sustained type II or high type III odontoid fractures due to abrupt deceleration of the head and continued forward torso momentum. Average peak force reached 1787.1 N at the neck at 50.3 milliseconds. Subsequently, the motion peaks occurred for the head relative to C3 reaching 15.2° for extension, 2.1 cm for upward translation, and 5.3 cm for horizontal compression, between 62 and 68 milliseconds. We identified impact to the upper forehead in the midline as a mechanism that produced odontoid fracture and associated atlas and ligamentous injuries similar to those observed in real-life trauma. We were not able to create odontoid fractures during impacts to the upper lateral side of the forehead or upper lateral side of the head. Dynamic odontoid fracture was caused by rapid deceleration of the head, which transferred load inferiorly combined with continued torso momentum, which caused spinal compression and anterior shear force and forward displacement of the axis relative to the atlas.

Plough fracture of the anterior arch of the atlas: a biomechanical investigation

"Plough" fracture, in which the odontoid ploughs through and causes a high-energy shear fracture of the anterior arch of the atlas, has been documented in clinical case studies and classified as clinically unstable. Our objectives were to develop a biomechanical model to simulate atlantal plough fracture and investigate injury mechanisms. Horizontally aligned head impacts into a padded barrier were simulated using a human upper cervical spine specimen (occiput through C3) mounted to a surrogate torso mass on a sled and carrying a surrogate head. We divided 13 specimens into 3 groups based upon head-impact location: upper forehead in the midline, upper lateral side of the forehead, and upper lateral side of the head. Post-impact fluoroscopy and anatomical dissection documented the injuries. Time-history biomechanical responses were determined for neck loads, accelerations, and motions. A single specimen sustained a plough fracture variant to the atlantal anterior arch due to impact to the upper forehead and continued forward torso momentum. Horizontal velocity of C3 at the time of forehead impact was 2.7 m/s. This specimen had an anteriorly displaced fracture fragment consisting of the inferior portion of the atlantal anterior arch together with multiple complete fractures of the axis. Peak force occurred first at the impact barrier (1,903.0 N; 47 ms) followed by the neck (1,715.9 N; 58 ms). Forward translation ended at 48 ms for the head and 72 ms for the C3 vertebra. Our present results, though preliminary, indicate that plough fracture of the anterior arch of the atlas likely occurred immediately following or simultaneously with associated axis fractures at approximately 58 ms following impact to the upper forehead. The present injury response data highlighted the role of load transfer from torso momentum to the upper cervical spine to produce anterior shear force and forward displacement of the dens and bony fragment of the anterior arch of the atlas relative to the C1 ring.

Axis ring fractures due to simulated head impacts

BackgroundWe investigated mechanisms of axis ring fractures due to simulated head impacts. MethodsOur model consisted of a human upper cervical spine specimen (occiput through C3) mounted to a surrogate torso mass on a sled and carrying a surrogate head. We divided 13 specimens into 3 groups based upon head impact location: upper forehead in the midline, upper lateral side of the forehead, and upper lateral side of the head. Post-impact fluoroscopy and anatomical dissection documented the injuries. Average occurrence times of the peak loads and accelerations were statistically compared (P<0.05) using ANOVA and Bonferroni pair-wise post-hoc tests. FindingsOf the 13 upper cervical spines tested, 5 specimens sustained axis ring fractures with the most common mechanism being impact to the upper left lateral side of the forehead. The first local force peaks at the impact barrier and neck and all peak head accelerations occurred between 18.0 and 22.8ms, significantly earlier than the absolute force peaks. The average peak neck loads reached 1761.2N and the axis ring fractures occurred within 50ms. InterpretationWe observed asymmetrical fractures of the axis ring including fractures of the superior and inferior facets, laminae, posterior wall of the vertebral body, pars interarticularis, and pedicles. The fracture patterns were related to the morphology of the axis as a transitional vertebra of the upper cervical spine. Understanding the mechanisms of axis ring fractures may help in choosing the optimal reduction technique and stabilization method based upon the specific fracture pattern.

Segmental torso masses in adolescent idiopathic scoliosis

BackgroundAdolescent idiopathic scoliosis is the most common type of spinal deformity whose aetiology remains unclear. Studies suggest that gravitational forces in the standing position play an important role in scoliosis progression, therefore anthropometric data is required to develop biomechanical models of the deformity. Few studies have analysed the trunk by vertebral level and none have performed investigations of the scoliotic trunk. The aim of this study was to determine the centroid, thickness, volume and estimated mass, for sections of the scoliotic trunk. MethodsExisting low-dose CT scans were used to estimate vertebral level-by-level torso masses for 20 female adolescent idiopathic scoliosis patients. ImageJ processing software was used to analyse the CT images and enable estimation of the segmental torso mass corresponding to each vertebral level. FindingsThe patients' mean age was 15.0 (SD 2.7) years with mean major Cobb angle of 52 (SD 5.9)° and mean patient weight of 58.2 (SD 11.6) kg. The magnitude of torso segment mass corresponding to each vertebral level increased by 150% from 0.6kg at T1 to 1.5kg at L5. Similarly, segmental thickness from T1–L5 increased inferiorly from a mean 18.5 (SD 2.2) mm at T1 to 32.8 (SD 3.4) mm at L5. The mean total trunk mass, as a percentage of total body mass, was 27.8 (SD 0.5) % which was close to values reported in previous literature. InterpretationThis study provides new anthropometric reference data on segmental (vertebral level-by-level) torso mass in adolescent idiopathic scoliosis patients, useful for biomechanical models of scoliosis progression and treatment.

Dynamics, stability, and actuation methods for powered compass gait walkers

In this paper, methods to achieve actively powered walking on level ground using a simple 2-dimensional walking model (compass-gait walker) are explored. The walker consists of 2 massless legs connected at the hip joint, a point mass at the hip, and an infinitesimal point mass at the feet. The walker is actuated either by applying equal joint torques at the hip and ankle, by an impulse applied at the toe off, immediately before the heel strike, or by the combination of both. It is shown that actuating the walker by equal joint torques at the hip and ankle on level ground is equivalent to the dynamics of the passive walker on a downhill slope. The gait cycle for the simplified walker model is determined analytically for a given initial stance angle. Stability of the gait cycle by an analytical approximation to the Jacobian of the walking map is calculated. The results indicate that the short-period cycle always has an unstable eigenvalue, whereas stability of the long-period cycle depends on selection of the initial stance angle. The effect of the torso mass by adding a third link attached at the hip joint is investigated. The torso link is kept in the vertical position by controlling the torque applied to it. The proportional-derivative control law is utilized to regulate the angular position error of the torso link. Using linearized dynamics for this walker, active control is applied to the ankle, which reduces the dynamics of the walker to the passive walker without the torso. The proposed walker is capable of producing stable walking while keeping the torso in an upright position.

Effects of acceleration level on lumbar spine injuries in military populations

Background contextClinical studies have indicated that thoracolumbar trauma occurs in the civilian population at its junction. In contrast, injury patterns in military populations indicate a shift to the inferior vertebral levels of the lumbar spine. Controlled studies offering an explanation for such migrations and the associated clinical biomechanics are sparse in literature. PurposeThe goals of this study were to investigate the potential roles of acceleration loading on the production of injuries and their stability characteristics using a human cadaver model for applications to high-speed aircraft ejection and helicopter crashes. Study designBiomechanical laboratory study using unembalmed human cadaver lumbar spinal columns. MethodsThoracolumbar columns from post-mortem human surrogates were procured, x-rays taken, intervertebral joints and bony components evaluated for degeneration, and fixed using polymethylmethacrylate. The inferior end was attached to a platform via a load cell and uniaxial accelerometer. The superior end was attached to the upper metal platform via a semi-circular cylinder. The pre-flexed specimen was preloaded to simulate torso mass. The ends of the platform were connected to the vertical post of a custom-designed drop tower. The specimen was dropped inducing acceleration loading to the column. Axial force and acceleration data were gathered at high sampling rates, filtered, and peak accelerations and inertia-compensated axial forces were obtained during the loading phase. Computed tomography images were used to identify and classify injuries using the three-column concept (stable vs. unstable trauma). ResultsThe mean age, total body mass, and stature of the five healthy degeneration-free specimens were 42 years, 73 kg, and 167 cm. The first two specimens subjected to peak accelerations of approximately 200 m/sec2 were classified as belonging to high-speed aircraft ejection-type and the other three specimens subjected to greater amplitudes (347–549 m/sec2) were classified as belonging to helicopter crash-type loadings. Peak axial forces for all specimens ranged from 4.8 to 7.2 kN. Ejection-type loaded specimens sustained single-level injuries to the L1 vertebra; one injury was stable and the other was unstable. Helicopter crash-type loaded specimens sustained injuries at inferior levels, including bilateral facet dislocation at L4–L5 and L2–L4 compression fractures, and all specimens were considered unstable at least at one spinal level. ConclusionsThese findings suggest that the severity of spinal injuries increase with increasing acceleration levels and, more importantly, injuries shift inferiorly from the thoracolumbar junction to lower lumbar levels. Acknowledging that the geometry and load carrying capacity of vertebral bodies increase in the lower lumbar spine, involvement of inferior levels in trauma sparing the superior segments at greater acceleration inputs agree with military literature of caudal shift in injured levels. The present study offers an experimental explanation for the clinically observed caudal migration of spinal trauma in military populations as applied to high-speed aircraft ejection catapult and helicopter crashes.

Trunk extensor muscle function in young and old women: A pilot study1

The purpose of this study was to document age-related alterations in trunk extensor strength and to compare these to changes in knee extensor strength over varying angles of muscle contraction. A secondary purpose was to compare age-related changes in trunk extensor endurance while statistically correcting for torso mass differences. Eighteen older (70 ± 7.3 years) and fifteen younger (22.1 ± 4.6 years) women volunteered for the study. Torso mass and trunk extension endurance (Modified- Sorenson test) were also evaluated. The results suggested that age-related torque production was both angle and muscle group dependent. Younger adults were 29% stronger in the knee and 23% stronger in the trunk extensors. Furthermore, the difference between age groups in knee extensor strength was 2.30 Nm/kg at 78 ◦ , but only 0.47 Nm/kg at 6 ◦ of knee flexion. This angle discrepancy was not evident in the trunk extensors. Following torso mass correction, trunk extension endurance time did not differ between ages (Young: 160.4 ± 65.8 vs. Old: 159.5 ± 71.9 sec, p = 0.99). Our study suggests that the elderly should focus on improving trunk extension strength rather than endurance. Also, knee extensor strength exercises should be emphasized between 60 ◦ and 108 ◦ of knee flexion in the elderly to combat the age-related loss of lower extremity strength.

Optimal jumping strategies from compliant surfaces: A simple model of springboard standing jumps

A simple model of standing dives is used to investigate optimal jumping strategies from compliant surfaces and applied to springboard diving. The human model consists of a massless leg actuated by knee torque, and a lumped torso mass centered above the leg. The springboard is modeled as a mass-spring system. Maximum jump height for a male and a female is calculated by controlling knee-torque activation level as a function of time. The optimization includes constraints on minimum and maximum knee angle, rate of change of normalized activation level, and contact duration. Simulation results for maximal springboard depression and diver takeoff velocity agree reasonably with experimental data, even though larger board tip velocities are necessarily predicted earlier during the contact period. Qualitatively similar multiple pulse knee-torque activation patterns are found over various conditions and are different from those in rigid-surface jumping. The model is less able to predict accurately jump height at high fulcrum number since jumpers may have difficulty behaving optimally at non-preferred fulcrum settings. If strength is proportional to the product of mass and leg length, increasing leg length is more effective in increasing jump height than is increasing mass.

Influence of Seat Properties on Occupant Dynamics in Severe Rear Crashes

Seat performance in retaining an occupant, transferring energy, and controlling neck responses is often questioned after severe rear crashes when fatal or disabling injury occur. It is argued that a stiffer seat would have improved occupant kinematics. However, there are many factors in occupant interactions with the seat. This study evaluates four different seat types in 26 and 32 mph (42 and 51 km/h), rear crash delta Vs. Two seats were yielding with k = 20 kN/m occupant load per displacement. One represented a 1970s yielding seat with j = 3.4°/kN frame rotation per occupant load, and 3 kN maximum load (660 Nm moment), and the other a high retention seat phased into production since 1997 with j = 1.4°/kN, and 10 kN maximum load (2200 Nm). Two seats were stiff with k = 40 kN/m. One represented a 1990s foreign benchmark with j = 1.8°/kN and a 7.7 kN maximum load (1700 Nm), and the other an all belts to seat (ABTS) with j = 1.0°/kN and 20 kN maximum load (4400 Nm). The crash was a constant acceleration of 11.8 g, or 14.5 g for 100 ms. Occupant interactions with the seat were modeled using a torso mass, flexible neck and head mass.By analysis of the equations of motion, the initial change in seatback angle (Δθ) is proportional to jk(y − x), the product jk and the differential motion between the vehicle (seat cushion) and occupant. The transition from 1970s–80s yielding seats to stronger seats of the 1990s involved an increase in k stiffness; however, the jk property did not change as frame structures became stronger. The yielding seats of the 1970s had jk = 68°/m, while the stiff foreign benchmark seat had jk = 72°/m. The foreign benchmark rotated about the same as the 1970s seat up to 50 ms in the severe rear crashes. While it was substantially stronger, it produced higher loads on the occupant, and the higher loads increased seatback rotations and neck responses. The ABTS seat had the lowest rotations but also caused high neck responses because of the greater loads on the torso. Neck displacement (d) is initially proportional to (k/mT) ∫∫ y, seat stiffness times the second integral of vehicle displacement divided by torso mass. As seat stiffness increases, head-torso acceleration, velocity, and neck displacement increase.This study shows that the jk seat property determines the initial seatback rotation in rear crashes. If a stronger seat has a higher stiffness, it rotates at higher loads on the occupant, reducing the overall benefit of the stronger frame, while increasing neck responses related to whiplash or neck extension prior to subsequent impacts. The aim of seat designs should be to reduce jk, provide pocketing of the pelvis, and give head-neck support for the best protection in severe rear crashes. For low-speed crashes, a low k is important to reduce early neck responses related to whiplash.

Seat Influences on Female Neck Responses in Rear Crashes: A Reason Why Women Have Higher Whiplash Rates

Since the earliest crash investigations, whiplash has been found to occur more often in women than men. This study addresses seat properties that may explain a reason for the higher rates in women, and changes in whiplash in general over the past two decades. Three exemplar seats were defined on the basis of seat stiffness ( k ) and frame rotation stiffness ( j ) for rearward occupant load. Stiff seats have k = 40 kN/m and j = 1.8°/kN representing a foreign benchmark loaded by a male. One yielding seat had k = 20 kN/m and j = 1.4°/kN simulating a high-retention seat (1997 Grand Prix) and another k = 20 kN/m and j = 3.4°/kN simulating a 1980s to 1990s yielding seat (1990 Buick Park Avenue). Constant vehicle acceleration for 100 msec gave delta-V of 6, 10, 16, and 24 km/h. The one-dimensional model included a torso mass loading the seatback with flexible neck and head mass. Based on biomechanical data and scaling, neck stiffness was 5 kN/m and 3 kN/m for the male and female, respectively. Based on validation tests, seat stiffness was 25% less with the female. Occupant dynamics were simulated in a step-forward solution based on the differential displacement between the head, torso, and seat up to head restraint contact. Neck responses were 30% higher in the female than male through most of the rear impact and are proportional to ( k F / m TF )/( k M / m TM ), which is the ratio of seat stiffness divided by torso mass for the female and male. Neck displacements were higher with the stiff seat than the 1990 C car seat for both the female and male. They peaked at 10 km/h and dropped off for higher severity crashes due to the shorter time to head contact. Neck displacements were greater in the female than male for the lowest severity crashes with the stiff and 1990 C car seats, when displacement was scaled for equal tolerance. The female in 1997 W car seat had the lowest neck displacements. Stiff seats increased neck displacements over the yielding seats of the 1980s in rear crashes. The trend is similar in men and women, but early neck displacements are greater in women because of a higher ratio of seat stiffness to torso mass. This implies that seat stiffness is not sufficiently low in proportion to the female mass in comparison to males. The j and k seat properties influence neck biomechanics and occupant dynamics, but k is important in determining early response differences between males and females.