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Finite state control is an established technique for the implementation of intention detection and activity co-ordination levels of hierarchical control in neural prostheses, and has been used for these purposes over the last thirty years. The first finite state controllers (FSC) in the functional electrical stimulation of gait were manually crafted systems, based on observations of the events occurring during the gait cycle. Subsequent systems used machine learning to automatically learn finite state control behaviour directly from human experts. Recently, fuzzy control has been utilised as an extension of finite state control, resulting in improved state detection over standard finite state control systems in some instances. Clinical experience over the last thirty years has been positive, and has shown finite state control to be an effective and intuitive method for the control of functional electrical stimulation (FES) in neural prostheses. However, while finite state controlled neural prostheses are of interest in the research community, they are not widely used outside of this setting. This is largely due to the cumbersome nature of many neural prostheses which utilise externally mounted gait sensors and FES electrodes. FES-based control of movement has been subject to the constraints of artificial sensor and FES actuator technologies. However, continued advances in natural sensors and implanted multi-channel stimulators are broadening the boundaries of artificial control of movement, driving an evolutionary process towards increasingly human-like control of FES-based gait rehabilitation systems. [ABSTRACT FROM AUTHOR]

In acute experiments the sciatic nerve of the rat is electrically stimulated to induce fatigue in the medial Gastrocnemius muscle. Fatigue tests are carried out using intermittent stimulation of different compartments (sequential) or a single compartment (synchronous) of the sciatic nerve. The activation of different compartments is achieved by dividing nerve fibres into subbundles and placing them in separate grooves in a multigroove electrode. The aim of the investigation is to quantify the effect of sequential contra synchronised stimulation in reducing muscle fatigue, with no overlap between compartments. Overlap between two compartments is calculated using the combined and individual forces from both compartments. Sequential stimulation of two and three compartments is investigated. There is a significant decrease of fatigue in sequential stimulation compared to synchronous. After 2 min of intermittent stimulation the force time level is significantly increased in sequential stimulation, than in synchronous stimulation. The rate of force time decrease is significantly slower in sequential stimulation than in synchronous stimulation. With sequential stimulation it takes significantly longer before the maximal force time is reached than with synchronous stimulation. [ABSTRACT FROM AUTHOR]

Control of paraplegic standing up was studied with respect to the limitation of the end-velocity of the knee joint when the patient reaches the upright position. Closed-loop on/off control of knee extensor muscle was compared with open-loop controlled standing up both in a model study and in paraplegic patients in a controlled model situation. Criteria were knee-end-velocity and knee extensor muscle activation time. Sensitivity of the system to additional arm support and (in the model study) to the dynamics of knee extensor muscle was studied. It is concluded that the control scheme may reduce knee-end velocity to about 40 per cent and knee extensor activation time to near 70 per cent of the respective open-loop values. [ABSTRACT FROM AUTHOR]

The control of a cyclical movement of the lower leg with electrical stimulation of the quadriceps muscles is formulated as an optimal control problem. The time integral of knee torque is taken as the optimisation criterion. As an additional condition, every cycle a certain reference maximum angle should be reached. A model study indicates that one stimulation burst per cycle at the maximum recruitment level is a suboptimal solution to this problem. To compensate for the influence of muscle fatigue, the burst time is adaptively adjusted by a discrete time PID-controller on the basis of the performance in the previous cycles. This strategy appeared to be successful in experimental tests. A considerable time difference (about 0.15 s) was found between the end of the stimulation burst and the tracking of the passive state trajectory, which satisfies the maximum angle condition. [ABSTRACT FROM AUTHOR]

The relationship between nerve stimulation, pulse amplitude and isometric muscle force was measured to investigate recruitment of motor units. Force addition experiments were performed to obtain insight in the intersection of motor unit groups recruited by different electrodes. Intrafascicular and extraneural multielectrode configurations were used for nerve stimulation. Experiments were performed on rats. The common peroneal nerve was stimulated and the forces of the tibial anterior and extensor digitorum longus muscles were measured isometrically. Recruitment was more stable for intrafascicular electrodes than for extraneural electrodes. Especially for intrafascicular electrodes no strict inverse recruitment was observed. Force addition experiments indicated that small overlap of recruited motor unit groups occurred more often for intrafascicular than for extraneural electrodes. [ABSTRACT FROM AUTHOR]