The effect of wrist angle and finger grip on maximum trigger pull force.

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.

Simulated chainsaw injury bone fracture data.

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.

Forensic application of inverse and reverse projection photogrammetry to determine subject location and orientation when both camera and subject move relative to the scene.

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.

Methodology for determining accidental versus intentional injury afflicted by a chainsaw.

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.

Neural Substrates of Muscle Co-contraction during Dynamic Motor Adaptation.

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.

Mechanical Aspects of Intervertebral Disc Injury and Implications on Biomechanics.

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.

Different adaptation rates to abrupt and gradual changes in environmental dynamics.

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.

Origin of directionally tuned responses in lower limb muscles to unpredictable upper limb disturbances.

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.

Effects of amplitude and predictability of perturbations to the arm on anticipatory and reactionary muscle responses to maintain balance.

Disturbances to balance arising from forces applied to the upper limb have received relatively little attention compared to disturbances arising from support surface perturbations. In this study we applied fast ramp perturbations to the hand in anterior, posterior, medial and lateral directions. The effects of perturbation predictability and amplitude on the postural response of upper limb, trunk and lower limb muscles were investigated.

Short-latency muscle response patterns to multi-directional, unpredictable perturbations to balance applied to the arm are context dependent.

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.

Segmental specificity in belly dance mimics primal trunk locomotor patterns.

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.

Control of finger forces during fast, slow and moderate rotational hand movements.

The goal of this study was to investigate the effect of speed on patterns of grip forces during twisting movement involving forearm supination against a torsional load (combined elastic and inertial load). For slow and moderate speed rotations, the grip force increased linearly with load torque. However, for fast rotations in which the contribution of the inertia to load torque was significantly greater than slower movements, the grip force-load torque relationship could be segmented into two phases: a linear ascending phase corresponding to the acceleration part of the movement followed by a plateau during deceleration.

A robotic interface to train grip strength, grip coordination and finger extension following stroke.

A two degree of freedom robotic interface was developed to assist with rehabilitation of three hand impairments following stroke: reduced grip strength, reduced finger extension, and loss of dexterity due to the lack of coordination between finger and wrist muscles. The design and performance characteristics of this interface, which takes advantage of an FPGA-based real-time platform, are discussed. The robotic interface is able to accurately render elastic and viscous loads.

Shared and specific independent components analysis for between-group comparison.

Independent component analysis (ICA) has been extensively used in individual and within-group data sets in real-world applications, but how can it be employed in a between-groups or conditions design? Here, we propose a new method to embed group membership information into the FastICA algorithm so as to extract components that are either shared between groups or specific to one or a subset of groups. The proposed algorithm is designed to automatically extract the pattern of differences between different experimental groups or conditions. A new constraint is added to the FastICA algorithm to simultaneously deal with the data of multiple groups in a single ICA run.

Independent activation in adjacent lumbar extensor muscle compartments.

The purpose of this study was to examine compartmentalization in human lumbar spine extensors. Structure and innervation of these muscles would suggest the possibility of more segmentally specific biomechanical functions than have been found in previous studies examining muscle activation patterns during simple spine bending and twisting tasks. We selected specialized tasks to more effectively investigate the degree of independent control possible within lumbar spine extensors.

Effects of a robot-assisted training of grasp and pronation/supination in chronic stroke: a pilot study.

Background: Rehabilitation of hand function is challenging, and only few studies have investigated robot-assisted rehabilitation focusing on distal joints of the upper limb. This paper investigates the feasibility of using the HapticKnob, a table-top end-effector device, for robot-assisted rehabilitation of grasping and forearm pronation/supination, two important functions for activities of daily living involving the hand, and which are often impaired in chronic stroke patients. It evaluates the effectiveness of this device for improving hand function and the transfer of improvement to arm function.

Modulation of arm stiffness in relation to instability at the beginning or the end of goal-directed movements.

In reaching to a target, stability near the target may be more critical for success than stability far from the target. Consequently, we postulated that high instability near the start would evoke less compensation than high instability near the target. Three stability conditions were implemented using a robot manipulandum: neutral stability everywhere (null field); high instability along the first half of the trajectory decreasing as the target was approached (start unstable); and instability increasing along the first half of the trajectory and remaining high as the target was approached (end unstable).

Concurrent adaptation of force and impedance in the redundant muscle system.

This article examines the validity of a model to explain how humans learn to perform movements in environments with novel dynamics, including unstable dynamics typical of tool use. In this model, a simple rule specifies how the activation of each muscle is adapted from one movement to the next. Simulations of multijoint arm movements with a neuromuscular plant that incorporates neural delays, reflexes, and signal-dependent noise, demonstrate that the controller is able to compensate for changing internal or environment dynamics and noise properties.

A protocol for measuring the direct effect of cycling on neuromuscular control of running in triathletes.

The direct effects of cycling on movement and muscle recruitment patterns (neuromuscular control) during running are unknown but critical to success in triathlon. We outline and test a new protocol for investigating the direct influence of cycling on neuromuscular control during running. Leg movement (three-dimensional kinematics) and muscle recruitment (surface electromyography, EMG) were compared between a control run (no prior exercise) and a 30-min transition run that was preceded by 20 min of cycling.

A technique for conditioning and calibrating force-sensing resistors for repeatable and reliable measurement of compressive force.

Miniature sensors that could measure forces applied by the fingers and hand without interfering with manual dexterity or range of motion would have considerable practical value in ergonomics and rehabilitation. In this study, techniques have been developed to use inexpensive pressure-sensing resistors (FSRs) to accurately measure compression force. The FSRs are converted from pressure-sensing to force-sensing devices.

CNS learns stable, accurate, and efficient movements using a simple algorithm.

We propose a new model of motor learning to explain the exceptional dexterity and rapid adaptation to change, which characterize human motor control. It is based on the brain simultaneously optimizing stability, accuracy and efficiency. Formulated as a V-shaped learning function, it stipulates precisely how feedforward commands to individual muscles are adjusted based on error.

How is somatosensory information used to adapt to changes in the mechanical environment?

Recent studies examining adaptation to unexpected changes in the mechanical environment highlight the use of position error in the adaptation process. However, force information is also available. In this chapter, we examine adaptation processes in three separate studies where the mechanical environment was changed intermittently.

Rapid adaptation to scaled changes of the mechanical environment.

We investigated adaptation to simple force field scaling to determine whether the same strategy is used as during adaptation to more complex changes in the mechanical environment. Subjects initially trained in a force field, consisting of a rightward lateral force with a parabolic spatial profile (PF). The field strength was then unexpectedly increased or decreased (DeltaPF) for repeated sets of five consecutive trials, with intervening PF trials.

Endpoint stiffness of the arm is directionally tuned to instability in the environment.

It has been shown that humans are able to selectively control the endpoint impedance of their arms when moving in an unstable environment. However, directional instability was only examined for the case in which the main contribution was from coactivation of biarticular muscles. The goal of this study was to examine whether, in general, the CNS activates the sets of muscles that contribute to selective control of impedance in particular directions.