Fatigue of intermittently stimulated quadriceps during imposed cyclical lower leg movements

During prolonged experiments the influence of knee angular velocity, and stimulation parameters (interpulse interval (IPI), duty cycle (DC), number of pulses per cycle (NP)) on fatigue-induced torque\ud decline of paralyzed human quadriceps was studied. Identification of torque-angle and -angular velocity was also performed. The overall loss of maximum torque (MT) and torque-time integral ('lTI) per cycle during sustained intermittent stimulation during isokinetic movement had a typical exponential decay reaching asymptotic values. Larger knee velocities resulted in a significantly faster and relative larger decay of MT and TTI. The rate and relative magnitude of fatigue during concentric contractions are in direct relation\ud to NP. The results may be valuable in the design of optimal control systems for FES which pursue minimization of muscle fatigue

An Engineering Approach towards Action Refinement

In the abstract modelling of distributed systems we may need methods to replace abstract behaviours by more concrete behaviours which are closer to implementation mechanisms. Furthermore, we may want these methods to preserve the correctness of such a replacement. This paper introduces an approach towards action refinement in which an abstract action is replaced by a concrete activity. This approach is based on a careful consideration of the `action' and `causality relation' architectural concepts, which enable an abstract action to be replaced by many alternative concrete activities in a general way. This approach is based on the application of abstraction rules to determine whether a concrete activity conforms to an abstract action, considering the context in which the concrete activity and the abstract action are embedde

The influence of voluntary upper body exercise on the performance of stimulated paralysed human quadriceps

In this study the influence of voluntary upper body exercise on the performance of stimulated paralysed human quadriceps was investigated in five subjects with spinal cord lesions in the thoracic spine. The experimental setup consisted of computer-controlled stimulation of the quadriceps using electrodes on the surface of the skin, a dynamometer for isometric or isokinetic loading of the lower leg, and a rowing ergometer for upper body exercise. In all subjects, quadriceps fatigue tests were conducted to study the influence of upper body exercise on knee torque during sustained continuous or intermittent stimulation of quadriceps. The relative asymptotic torque appeared to be significantly higher with the presence of upper body exercise than without. This was consistently found both between trials (starting with or without upper body exercise) as well as within trials, when upper body exercise was started or stopped during the trial. No significant influence of upper body exercise on the time constant of initial torque decline was found

On Engineering Support for Business Process Modelling and Redesign

Currently, there is an enormous (research) interest in business process redesign (BPR). Several management-oriented approaches have been proposed showing how to make BPR work. However, detailed descriptions of empirical experience are few. Consistent engineering methodologies to aid and guide a BPR-practitioner are currently emerging. Often, these methodologies are claimed to be developed for business process modelling, but stem directly from information system design cultures. We consider an engineering methodology for BPR to consist of modelling concepts, their representation, computerized tools and methods, and pragmatic skills and guidelines for off-line modelling, communicating, analyzing, (re)designing\ud business processes. The modelling concepts form the architectural basis of such an engineering methodology. Therefore, the choice, understanding and precise definition of these concepts determine the productivity and effectiveness of modelling tasks within a BPR project. The\ud current paper contributes to engineering support for BPR. We work out general issues that play a role in the development of engineering support for BPR. Furthermore, we introduce an architectural framework for business process modelling and redesign. This framework consists of a coherent set of modelling concepts and techniques on how to use them. The framework enables the modelling of both the structural and dynamic characteristics of business processes. We illustrate its applicability by modelling a case from service industry. Moreover, the architectural framework supports abstraction and refinement techniques. The use of these techniques for a BPR trajectory are discussed

Cycle-to-cycle control of swing phase of paraplegic gait induced by surface electrical stimulation

Parameterised swing phase of gait in paraplegics was obtained using surface electrical stimulation of the hip flexors, hamstrings and quadriceps; the hip flexors were stimulated to obtain a desired hip angle range, the hamstrings to provide foot clearance in the forward swing, and the quadriceps to acquire knee extension at the end of the swing phase. We report on two main aspects; optimisation of the initial stimulation parameters, and parameter adaption (control). The initial stimulation patterns were experimentally optimised in two paraplegic subjects using a controlled stand device, resulting in an initial satisfactory swinging motion in both subjects. Intersubject differences appeared in the mechanical output (torque joint) per muscle group. During a prolonged open-loop controlled trial with the optimised but unregulated stimulation onsets and burst duration for the three muscle groups, the hip angle range per cycle initially increased above the desired value and subsequently decreased below it. The mechanical performance of the hamstrings and quadriceps remained relatively unaffected. A cycle-to-cycle controller was then designed, operating on the basis of the hip angle ranges obtained in previous swings. This controller successfully adapted the burst duration of the hip flexors to maintain the desired hip angle range

The feasibility of posture and movement detection by accelerometry

The discrimination of postures and movements using a minimal set of uniaxial accelerometers was investigated. Postures and movements were distinguished on the bitsis of the high-pm filtered, rectified and low pass filtered signal of one accelerometer. Postures were discriminated by combining the constant valued signals of the accelerometers, mounted on different segments of the body. One sensor mounted ndiully on the trunc and one mounted radially or tangentially on the upper leg appeared to be suficient to discriminate shnding, sitting and lying. Methods are proposed for the discrimination of different cyclical movements

Fatigue of intermittently stimulated human quadriceps during imposed cyclical lower leg movements

In this study the torque output of intermittently stimulated paralyzed human knee extensor muscles during imposed isokinetic cyclical lower leg movements was investigated in four paraplegic subjects. During prolonged (10 min) experiments the influence of knee angular velocity and stimulation parameters on fatigue-induced torque decline was studied. Pulse width and amplitude were set to obtain maximal recruitment. The cycle time was maintained constant at 2 s, comparable to a walking cycle. The maximum torque and averaged torque per cycle were estimated to determine the muscle's performance during sustained intermittent stimulation. The overall loss in time of these parameters had a typical exponential decay reaching asymptotic values. Additionally, larger knee velocities resulted in a significantly faster and relatively larger decay of maximum and averaged torque. Also, the rate and relative decrement of torque output during concentric contractions increased with increasing number of pulses in a cycle. Identification trials, determining the (isometric) torque-angle and (isokinetic) torque-angular velocity relation, were performed. The relations appeared to change due to fatigue. The results might be valuable in the design of optimal control systems for functional electrical stimulation which pursue minimization of muscle fatigue. They may contribute to the derivation of a cost criterion, describing muscle fatigue as a function of both joint movement and stimulation parameters

Adaptive neural network control of fes-induced cyclical lower leg movements

As a first step to the control of paraplegic gait by functional electrical stimulation (FES), the control of the swinging lower leg is being studied. This paper deals with a neural control system, that has been developed for this case. The control system has been tested for a model of the swinging lower leg using computer simulations. The neural controller was trained by supervised learning (SL) and by backpropagation through time (BTT). The performance of the controller with random initial weights was poor after training with BTT and fair after SL. BTT training of the neural controller with weights, which had been initialized by SL, resulted in good control. Training with BTT thus improved the performance of the controller that initially had been trained by SL. An adaptive neural control system based on BTT has been proposed and partially tested. The controller adapted relatively fast to the change of an important model parameter