Control of a wrist joint motion simulator: a phantom study

The presence of muscle redundancy and co-activation of agonist-antagonist pairs in vivo makes the optimization of the load distribution between muscles in physiologic joint simulators vital. This optimization is usually achieved by employing different control strategies based on position and/or force feedback. A muscle activated physiologic wrist simulator was developed to test and iteratively refine such control strategies on a functional replica of a human arm. Motions of the wrist were recreated by applying tensile loads using electromechanical actuators. Load cells were used to monitor the force applied by each muscle and an optical motion capture system was used to track joint angles of the wrist in real-time. Four control strategies were evaluated based on their kinematic error, repeatability and ability to vary co-contraction. With kinematic errors of less than 1.5°, the ability to vary co-contraction, and without the need for predefined antagonistic forces or muscle force ratios, novel control strategies – hybrid control and cascade control – were preferred over standard control strategies – position control and force control. Muscle forces obtained from hybrid and cascade control corresponded well with in vivo EMG data and muscle force data from other wrist simulators in the literature. The decoupling of the wrist axes combined with the robustness of the control strategies resulted in complex motions, like dart thrower’s motion and circumduction, being accurate and repeatable. Thus, two novel strategies with repeatable kinematics and physiologically relevant muscle forces are introduced for the control of joint simulators

Shoulder muscle electromyographic activity and stiffness in patients with frozen shoulder syndrome: six-month follow-up study

This study evaluated changes in shoulder muscle isometric endurance, deltoideus and trapezius muscle electromyographic activity (EMG) and stiffness in patients with frozen shoulder syndrome (FSS) before and after manipulation under general anaesthesia (MUA). Eighteen FSS patients with mean age of 53±9 years participated. Isometric endurance of shoulder muscles was characterized by endurance test time and deltoideus and trapezius muscles EMG activity that were assessed by electromyograph during weight holding in hand until exhaustion. Stiffness of deltoideus and trapezius muscles was assessed by myotonometer (MYOTON-3). Patients were screened by self-administered shoulder rating questionnaire (SRQ). Data was collected before one and six months after MUA. Six months aft er MUA endurance test time remained reduced (p<0.05) for the involved extremity as compared with the uninvolved extremity. Deltoideus and trapezius muscle EMG activity decreased (p<0.05) at the end of the endurance test, whereas in the beginning of the endurance test the trapezius muscle EMG was lower (p<0.05) for the involved extremity. Deltoideus and trapezius muscle stiffness did not differ (p<0.05). SRQ score points decreased (p<0.05) one and six months aft er MUA. In conclusion, six months after MUA the shoulder muscle EMG activity and stiffness for the involved extremity was normalized in patients with FSS

The reality of myoelectric prostheses : understanding what makes these devices difficult for some users to control

Users of myoelectric prostheses can often find them difficult to control. This can lead to passive-use of the device or total rejection, which can have detrimental effects on the contralateral limb due to overuse. Current clinically available prostheses are ‘open loop’ systems, and although considerable effort has been focused on developing biofeedback to “close the loop”, there is evidence from laboratory-based studies that other factors, notably improving predictability of response, may be as, if not more, important. Interestingly, despite a large volume of research aimed at improving myoelectric prostheses, it is not currently known which aspect of clinically available systems has the greatest impact on overall functionality and everyday usage. A protocol has therefore been designed to assess EMG skill of the user and predictability of the prosthesis response as significant parts of the control chain, and to relate these to functionality and everyday usage. Here we present the protocol and results from early pilot work. A set of experiments has been developed. Firstly to characterize user skill in generating the required level of EMG signal, as well as the speed with which users are able to make the decision to activate the appropriate muscles. Secondly, to measure unpredictability introduced at the skin-electrode interface, in order to understand the effects of the socket mounted electrode fit under different loads on the variability of time taken for the prosthetic hand to respond. To evaluate prosthesis user functionality, four different outcome measures are assessed. Using a simple upper limb functional task prosthesis users are assessed for (1) success of task completion, (2)task duration, (3) quality of movement, and (4) gaze behavior. To evaluate everyday usage away from the clinic, the symmetricity of their real-world arm use is assessed using activity monitoring. These methods will later be used to assess a prosthesis user cohort, to establish the relative contribution of each control factor to the individual measures of functionality and everyday usage (using multiple regression models). The results will support future researchers, designers and clinicians in concentrating their efforts on the area which will have the greatest impact on improving prosthesis use

Ergonomics of the Operative Field in Paediatric Minimal Access Surgery

Imperial Users onl

Simulation of motor unit action potential recordings from intramuscular multichannel scanning electrodes

International audienceMultichannel intramuscular EMG (iEMG) recordings provide information on motor neuron behaviour, muscle fiber (MF) innervation geometry and, recently, have been proposed as means for establishing human-machine interfaces. Objective: in order to provide a reliable benchmark for computational methods applied to such recordings, we propose a simulation model for iEMG signals acquired by intramuscular multi-channel electrodes. Methods: we propose a number of modifications to the existing iEMG simulation methods, such as farthest point sampling for more uniform motor unit in-nervation centers distribution in the muscle cross-section, fiber-neuron assignment algorithm, motor neuron action potential propagation delay modelling and a linear model for multichannel recordings simulation. The proposed approach is also extended to gradually shifting (scanning) electrodes. Results: we provide representative applications of this model to the validation of methods for the estimation of motor unit territories, and for iEMG decomposition. Moreover, we extend this model to a full multichannel iEMG simulator using classical linear EMG modelling and existing approaches to the generation of motor neuron discharge sequences. Conclusions: the obtained simulation model provides physiologically accurate MUAPs across entire motor unit territories and for various electrode configurations. Significance: it can be used for the development and evaluation of mathematical methods for multichannel iEMG processing and analysis

Optimizing the Rehabilitation of Elbow Lateral Collateral Ligament Injuries

Elbow lateral collateral ligament (LCL) injuries frequently arise following trauma, and can result in disabling instability. Typically such injuries are managed with immobilization followed by a graduated exercise regime; however there is minimal biomechanical evidence to support current treatment protocols. This investigation examines the in vitro effectiveness of several rehabilitation techniques using a custom elbow motion simulator. It was found that active range of motion is safest in the overhead position (n = 7). Early motion in this position may reduce the incidence of elbow stiffness without compromising ligament healing following LCL injury. Forearm pronation and active motion stabilize the LCL-deficient elbow, while varus positioning worsens instability. It was also found that a hinged elbow orthosis did not significantly improve in vitro elbow stability following LCL injury (n = 7). However, such orthoses may be useful in keeping the forearm in the more stable pronated position. Future research directions are proposed, with suggestions on applying this methodology to other elbow injuries

The Psychophysiology of Real-Time Financial Risk Processing

A longstanding controversy in economics and finance is whether financial markets are governed by rational forces or by emotional responses. We study the importance of emotion in the decisionmaking process of professional securities traders by measuring their physiological characteristics, e.g., skin conductance, blood volume pulse, etc., during live trading sessions while simultaneously capturing real-time prices from which market events can be defined. In a sample of 10 traders, we find significant correlation between electrodermal responses and transient market events, and between changes in cardiovascular variables and market volatility. We also observe differences in these correlations among the 10 traders which may be systematically related to the traders' levels of experience.

Real-time processing of physiological signals for feedback control

Extensive studies about neural mechanisms involved in insect flight control have been carried out. Adaptive control of locomotion requires integration of salient sensory cues with ongoing motor activity. During flight, inputs received by an organism through sensory organs are processed by the central nervous system (CNS) and the integrated output thus obtained plays a significant role in controlling the wing phase shifts and flight muscle depressor asymmetries associated with adaptive flight maneuvers. The resulting maneuvers, in turn, bring a change in the insect’s sensory environment, thereby closing the feedback loop. Research on insect flight has been carried out using immobile preparations (tethered) and mobile preparations (free flight – untethered). There are pros and cons associated with the tethered and the untethered approach. The tethered approach, however, provides an easier way to study the CNS and its role in motor control of flight. Insects such as locusts and moths exhibit pertinent wing phase shifts and asymmetries in depressor muscles. For locusts constant wing phase shifts and m97 (forewing first basalar depressor muscle) depressor asymmetries have been observed during adaptive flight maneuvers making this a useful system for creation of behaviorally appropriate visual feedback. A method that utilizes asymmetrical timing of bilateral depressor muscles, the forewing first basalars (m97), of the locust to close a visual feedback loop in a computer-generated flight simulator is presented here. The method converts the time difference between left and right m97s to analog voltage values. Analog voltage values can be acquired using an open-loop experimental protocol (visual motion controlled by the experimenter), or can be used to control closed-loop experiments (muscle activity controls the visual stimuli) experiments. We recorded electromyographic (EMG) activity from right and left m97 muscles. On testing this circuit with real animals, we were able to detect the spike time difference and convert it to voltage values. These voltage values were utilized to control the presentation of a stimulus in a closed-loop environment. The feedback circuit presented here may be used in conjunction with the flight simulator(s) to understand the neural mechanisms involved in control of insect flight and provide further understanding of general mechanisms of neural control of behaviour