We evaluated Virtual CRASH motion output as input to MADYMO for assessing risk of injury to rear seat occupants of a vehicle involved in a three-vehicle collision. The vehicle accelerometer records captured by the vehicle's EDR served as a reference. We determined that Virtual CRASH can faithfully reproduce crash scene evidence and general vehicle motion, but it overestimates peak accelerations during impacts, which would lead to overestimating the risk of injuries. Although EDR records provide a reliable input for MADYMO, since they are only 0.3 s in duration and represent vehicle motion in the reference frame of the vehicle, their utility in reconstructing events following an impact is limited. We demonstrate the utility of combining Virtual CRASH with MADYMO to reconstruct the entire sequence of events during the collision and accurately assess the risk of injury to the rear seat occupants of the most damaged vehicle.

There is a debate over whether the effect of prone restraint on respiration can lead to cardiac arrest. In itself, the prone or prone restrained posture does not likely compromise ventilation to any clinically significant degree for a detainee who is passive and calm, as a number of prone restraint studies have shown. However, these studies were not able to replicate an anxious, distressed or intoxicated (alcohol or drugs) detainee who is struggling and being actively held down. This review examines the physiology and biomechanics of respiration, highlighting the differences between upright position respiration and prone respiration and the effect of restraint on respiration. In addition, the findings of research on the effects of struggling, obesity, anxiety or panic and drug intoxication on the consequent carbon dioxide (CO2) production and the work of breathing are presented. The limitations which each of these factors place on the ability to remove CO2 from the blood are discussed. The evidence suggests that severe respiratory or metabolic acidosis could arise as the result of the combined effects of several factors and that cardiac arrest, if it occurs, would be more likely due to hypercapnia than hypoxia.

A forensic investigation into a shot fired by a handgun may require analysis of the body posture of the shooter or an opinion of whether the shot was deliberate or inadvertent. Determining the amount of force which can be applied to the trigger or the direction in which the handgun was pointing could be critical to the investigation. Studies investigating the effect of arm posture on whole hand maximum grip force suggest that maximum index finger force will be highly dependent on wrist angle and finger grip. The present study was designed to quantify the effect of these factors on maximum index finger trigger pull force. We found that even under almost optimal conditions, trigger pull force is substantially reduced with wrist flexion and is significantly lower with a finger pad grip compared to a finger hook grip. Our results indicate that for wrist flexion angles greater than 60°, maximum trigger pull force dropped by 50 % for male subjects and by 38 % for female subjects compared to the neutral or extended wrist. Other studies have shown that when a firm grip cannot be established, maximum index finger force can be less than 30 % of what we measured. Thus, maximum trigger pull forces could be below 22.9 N (5.1 lb) for male subjects and 19.0 N (4.5 lb) for female subjects in certain scenarios. If a subject is unable to get a firm grip on a handgun and the arm is in an awkward posture, it is possible that the subject would not be able to exert sufficient index finger force to overcome the trigger weight of many handguns.

Background: The force required for a sword to penetrate the human chest was identified as an important issue for the defense in a case of homicide by stabbing. Previous literature on penetration force had tested knives but not swords. Objective: The objective of the current study was to determine the peak force during penetration of a surrogate for human tissue with a ceremonial sword. Methods: The sword was secured to an MK-10 Tensile Tester and forced to penetrate a pork rib cut at speeds of 350 mm/min and 1100 mm/min, including both regions of rib and cartilage for pork ribs without skin or covered with a layer of porcine skin. Results: In the case of the pork ribs without skin, the mean peak penetration force at a speed of 350 mm/min was 11.0 N compared to a mean of 10.5 N at a speed of 1100 mm/min. The distributions of peak penetration forces at the two speeds were not significantly different. In the case of the pork ribs covered with porcine skin, the mean peak penetration force at a speed of 350 mm/min was 50.0 N compared to a mean of 47.6 N at a speed of 1100 mm/min. The distributions of peak penetration forces at the two speeds were again not significantly different. Conclusion: Forces of less than 50 N would be required for a ceremonial sword to penetrate the tissues of the human chest, although there is a risk of penetration for forces as low as 5 N when the effect of the porcine skin is not considered. Furthermore, the force required for penetration did not vary significantly over a three-fold speed of penetration.

Synthetic skin produced by SynDaver®, currently used primarily in medical testing and training applications, may be suitable as a surrogate for human skin in forensic investigations. To determine how accurately the company's synthetic skin, SynTissue®, could mimic the mechanical properties of human skin, tests were conducted to measure its elastic modulus and resistance to laceration. Test results were compared to published data acquired from tensile tests conducted on human scalp and impacts with blunt objects on porcine heads. The stress vs strain relation for SynTissue® 8 N corresponded closely to that of the human scalp. Deformations similar to skin lacerations were observed when SynTissue® was subjected to blunt object impacts, at forces in the range of those reported for lacerations of cadaver and porcine heads. However, the published data are insufficient to unequivocally assess the suitability of SynTissue® for forensic investigations of lacerations. Moreover, there are features of the SynTissue® impact deformations that can provide useful information even if the laceration threshold turns out to be lower than that of human skin.

An important tactile function is the active detection of small-scale features, such as edges or asperities, which depends on fine hand motor control. Using a resting-state fMRI paradigm, we sought to identify the functional connectivity of the brain network engaged in mapping tactile inputs to and from regions engaged in motor preparation and planning during active touch. Human participants actively located small-scale tactile features that were rendered by a computer-controlled tactile display. To induce rapid perceptual learning, the contrast between the target and the surround was reduced whenever a criterion level of success was achieved, thereby raising the task difficulty. Multiple cortical and subcortical neural connections within a parietal-cerebellar-frontal network were identified by correlating behavioral performance with changes in functional connectivity. These cortical areas reflected perceptual, cognitive, and attention-based processes required to detect and use small-scale tactile features for hand dexterity.

Forensic analysis is often required to determine the cause of an injury. Data for this purpose were acquired by simulating an injury to a limb inflicted by a chainsaw. A surrogate forearm was constructed from gel and a bone simulant. A series of 10 arms were severed under different conditions of chainsaw operation, arm position and arm resistance. The bone fracture force was determined from force records acquired with a force plate which supported the test rig holding the arm. A break wire in the arm signalled the time of fracture. The data set constitutes the reaction force registered by the force plate and the break wire signal. Both signals were digitally sampled at 1000 Hz. Photographs of the proximal portion of each severed arm were taken with a digital camera and are included in the data set. This data set is of interest to forensic investigators considering injuries inflicted by power tools. The data provide a benchmark for planning tests of simulated injuries. They can also be compared to experiments carried out on cadaveric specimens to determine the accuracy of such simulations. This article is being submitted as a co-submission with the following article, G.T. Desmoulin, T.E. Milner, Methodology for determining accidental versus intentional injury afflicted by a chainsaw. Forensic Science International. https://doi.org/10.1016/j.forsciint.2021.110993.

We present a case study of a mountain bicycle accident captured by the rider's chest-mounted action camera. The objective of the investigation was to determine the orientation of the bicycle relative to the ground and the location of the rider's center of gravity relative to the bicycle. The problem faced in the investigation was that the camera was moving relative to the scene and rider, and the bicycle was moving relative to the camera. Inverse photogrammetry was used to determine the location and orientation of the camera relative to the scene. Reverse projection photogrammetry applied to an exemplar bicycle provided an estimate of the location and orientation of the bicycle relative to the camera. The rider's position and orientation relative to the camera were estimated by comparing synchronized side views and chest-mounted action camera views of the rider's movements, recorded during a trail descent prior to the accident.

Computer-generated models have revolutionized how reconstructions of violent events, such as police use of force, are both performed and visualized. Yet, many experts in the legal and forensic disciplines do not understand them at a level required to use them effectively or create credible arguments supporting their findings. Simply put, models are a simplification of reality. Hence, models permit human programmers to specify the simplified behavior of a system. Since model parameters dictate the system's behavior, the programmer must document and provide justification for the selection of model parameters. The model structure, together with the selected parameters, form the backbone supporting the forensic investigator's conclusions. This paper will begin with an overview of the usefulness of models in forensic investigations and follow with an example of how a model is constructed and applied in use of force cases. The selected cases are particularly relevant to incidents commonly encountered in law enforcement, frequently leading to litigation.

Forensic analysis is often required to determine whether an injury was inflicted intentionally or accidentally. We have developed a method for addressing this issue in the case of an injury to a limb inflicted by a chainsaw. We discuss the potential use of this methodology to the more general case of injuries inflicted by power tools.

Despite significant progress in aircraft crashworthiness, unexpected and oddly serious injuries are sometimes seen in otherwise survivable incidents. In one such case, a small fixed-wing aircraft c...

As we learn to perform a motor task with novel dynamics, the central nervous system must adapt motor commands and modify sensorimotor transformations. The objective of the current research is to identify the neural mechanisms underlying the adaptive process. It has been shown previously that an increase in muscle co-contraction is frequently associated with the initial phase of adaptation and that co-contraction is gradually reduced as performance improves. Our investigation focused on the neural substrates of muscle co-contraction during the course of motor adaptation using a resting-state fMRI approach in healthy human subjects of both genders. We analyzed the functional connectivity in resting-state networks during three phases of adaptation, corresponding to different muscle co-contraction levels and found that change in the strength of functional connectivity in one brain network was correlated with a metric of co-contraction, and in another with a metric of motor learning. We identified the cerebellum as the key component for regulating muscle co-contraction, especially its connection to the inferior parietal lobule, which was particularly prominent in early stage adaptation. A neural link between cerebellum, superior frontal gyrus and motor cortical regions was associated with reduction of co-contraction during later stages of adaptation. We also found reliable changes in the functional connectivity of a network involving primary motor cortex, superior parietal lobule and cerebellum that were specifically related to the motor learning.SIGNIFICANCE STATEMENT It is well known that co-contracting muscles is an effective strategy for providing postural stability by modulating mechanical impedance and thereby allowing the central nervous system to compensate for unfamiliar or unexpected physical conditions until motor commands can be appropriately adapted. The present study elucidates the neural substrates underlying the ability to modulate the mechanical impedance of a limb as we learn during motor adaptation. Using resting-state fMRI analysis we demonstrate that a distributed cerebellar-parietal-frontal network functions to regulate muscle co-contraction with the cerebellum as its key component.

Study Design. This article comprises a review of the literature. Objective. The purpose of this study was to elucidate the different types of structural failures exhibited in intervertebral discs (IVDs), summarize their potential causes with respect to mechanical loading conditions and the consequences on cell homeostasis and biomechanics. Summary of Background Data. Many studies have been performed to gain insight into how discogenic back pain progresses in humans both in vitro and in vivo as well as in animal disc models. However, there is a major need to summarize the common factors which initiate the structural failures observed in IVDs and the typical biomechanical changes. This work could help in developing mechanisms aiming to restore the biochemical and biomechanical balance of IVDs. Methods. The different types of structural failures encountered in IVDs were reviewed from published literature. The types of mechanical loading causing these injuries and their physiological and biomechanical consequences were then summarized and linked to ongoing research in this area. Results. The most prominent structural failures associated with IVDs are annulus tears, disc prolapse, endplate damage, disc narrowing, radial bulging, and osteophyte formation in the vertebrae. IVDs were found to be vulnerable to compression, flexion, axial rotation, and complex loading mechanisms through single impact, cyclical, and continuous loading. However, chronic loadings had a more damaging impact on the spine. Significant consequences include imbalance of metabolic enzymes and growth factors, alteration in stress profiles of IVDs and a decrease in mechanical stiffness resulting in impaired biomechanics of the spine. Conclusion. The mode of loading has an important impact on the severity and nature of failures seen in IVDs and the resulting consequences to biomechanics. However, further research is necessary to better understand to the mechanisms that link injury to degeneration and regeneration of IVD tissues. Level of Evidence: 3

Adaptation to an abrupt change in the dynamics of the interaction between the arm and the physical environment has been reported as occurring more rapidly but with less retention than adaptation to a gradual change in interaction dynamics. Faster adaptation to an abrupt change in interaction dynamics appears inconsistent with kinematic error sensitivity which has been shown to be greater for small errors than large errors. However, the comparison of adaptation rates was based on incomplete adaptation. Furthermore, the metric which was used as a proxy of the changing internal state, namely the linear regression between the force disturbance and the compensatory force (the adaptation index), does not distinguish between internal state inaccuracy resulting from amplitude or temporal errors. To resolve the apparent inconsistency, we compared the evolution of the internal state during complete adaptation to an abrupt and gradual change in interaction dynamics. We found no difference in the rate at which the adaptation index increased during adaptation to a gradual compared to an abrupt change in interaction dynamics. In addition, we separately examined amplitude and temporal errors using different metrics, and found that amplitude error was reduced more rapidly under the gradual than the abrupt condition, whereas temporal error (quantified by smoothness) was reduced more rapidly under the abrupt condition. We did not find any significant change in phase lag during adaptation under either condition. Our results also demonstrate that even after adaptation is complete, online feedback correction still plays a significant role in the control of reaching.

Unpredictable forces which perturb balance are frequently applied to the body through interaction between the upper limb and the environment. Lower limb muscles respond rapidly to these postural disturbances in a highly specific manner. We have shown that the muscle activation patterns of lower limb muscles are organized in a direction specific manner which changes with lower limb stability. Ankle muscles change their activity within 80 ms of the onset of a force perturbation applied to the hand which is earlier than the onset of changes in ground reaction force, ankle angle or head motion. The latency of the response is sensitive to the perturbation direction. However, neither the latency nor the magnitude of the response is affected by stiffening the arm even though this alters the magnitude and timing of motion of the body segments. Based on the short latency, insensitivity of the change in ankle muscle activation to motion of the body segments but sensitivity to perturbation direction we reason that changes in ankle muscle activation are most likely triggered by sensory signals originating from cutaneous receptors in the hand. Furthermore, evidence that the latency of changes in ankle muscle activation depends on the number of perturbation directions suggests that the neural pathway is not confined to the spinal cord.

Belly dance was used to investigate control of rhythmic undulating trunk movements in humans. Activation patterns in lumbar erector spinae muscles were recorded using surface electromyography at four segmental levels spanning T10 to L4. Muscle activation patterns for movement tempos of 2 Hz, 3 Hz, and as fast as possible (up to 6 Hz) were compared to test the hypothesis that frequency modulates muscle timing, causing pattern changes analogous to gait transitions. Groups of trained and untrained female subjects were compared to test the hypothesis that experience modifies muscle coordination patterns and the capacity for selective motion of spinal segments. Three distinct coordination patterns were observed. An ipsilateral simultaneous pattern (S) and a diagonal synergy (D) dominated at lower frequencies. The S pattern was selected most often by novices and resembled the standing wave of activation underlying the alternating lateral trunk bending in salamander trotting. At 2 Hz, most trained subjects selected the D pattern, suggesting a greater capacity for segmental specificity compared with untrained subjects. At 3-4 Hz, there emerged an asynchronous pattern (A) analogous to the rostral-caudal traveling wave in salamander and lamprey swimming. The neural networks and mechanisms identified in primitive vertebrates, such as chains of coupled oscillators and segmental crossed inhibitory connections, could explain the patterns observed in this study in humans. Training allows modification of these patterns, possibly through improved capacity for selectively exciting or inhibiting segmental pattern generators.NEW & NOTEWORTHY Belly dance provides a novel approach for studying spinal cord neural circuits. New evidence suggests that primitive locomotor circuits may be conserved in humans. Erector spinae activation patterns during the hip shimmy at different tempos are similar to those observed in salamander walking and swimming. As movement frequency increases, a sequential pattern similar to lamprey swimming emerges, suggesting that primal involuntary control mechanisms dominate in fast lateral rhythmic spine undulations even in humans.

A number of studies have shown that sensory inputs from the hand can have a profound effect in stabilizing upright posture. This suggests that the central nervous system can extract information about body motion and external forces acting on the body from cutaneous sensory signals. We have recently shown that the central nervous system determines the direction of an unpredictable force applied to the hand so rapidly that it is able to activate ankle muscles in advance of the perturbing effect that this force has at the ankles. In this study we investigate whether this rapid change in activation of lower limb muscles is an invariant response determined by the pattern of somatosensory information arising from sensory receptors in the hand or whether it adapts to changes in postural stability. We manipulated lateral stability of upright stance by changing stance width which had no effect on the activation of upper limb muscles or hand kinematics, but produced profound changes in the activation patterns of lower limb muscles when perturbations were in the medial/lateral direction without affecting the activation patterns of muscles when perturbations were in the anterior/posterior direction.

When the arm of a standing human is perturbed in an unpredictable direction, postural muscles are activated at latencies as short as 50–110 ms. While the motion of the body clearly progresses in hand-to-leg sequence, there is no systematic muscle activation sequence from the arm to the leg muscles, suggesting that the activation of the muscles is not likely the result of local stretch reflexes. In fact, the lower limb muscles are activated before the upright posture is significantly disturbed. The short-latency activation amplitude and the activation probability are clearly tuned to the direction of the arm perturbation for both rostral and caudal muscles. The effect of central set on the short-latency response has been investigated by manipulating the predictability of the perturbations. Possible underlying neural mechanisms have been discussed.