Control of upper-limb functional neuromuscular electrical stimulation

Abstract

Functional electrical stimulation (FES) is the name given for the use of neuromuscular electrical stimulation to achieve patterns of induced movement which are of functional benefit to the user. System are available that use FES to aid persons who have suffered an insult to the motor control region of the brain and been left with movement impairment.

The aim of this research was to investigate methods of providing an FES system that could have a beneficial effect in restoring arm function. The techniques for applying upper-limb stimulation are well established, however the methods of controlling it to provide functional use remain lacking. This is because upper-limb movement can be difficult to measure and quantify as the starting point for any movement may not be well defined. Moreover the movements needed to complete a useful function such as reaching and grasping requires the coordinated control of a number of muscle groups, and that relies on being able to track the position of the limb. Effective control of FES for the arm requires reliable feedback about the position and state of the limb.

Electromyograms (EMG) are a measure of the very small electrical signals that are emitted whenever a muscle is ‘fired’ to move. EMG can be used to detect muscle activity and so can be a useful feedback control input. It does however have a number of drawbacks that this research sought to address by combining the method with external motion sensors. The intension had been to use the motion sensors to track the position of the limb and then use the EMG measurements to detect the wearer’s movements. FES could then be used to assist the wearer in making a desired movement. Initial studies were done to separately investigate the motion sensing and the EMG measurement components of the system. However before these could be combined a more interesting observation was made relating to bioimpedance.

A study of bioimpedance measurements found a relationship between tissue impedance changes and muscle activity. Different methods for measuring bioimpedance where investigated and the results compared, before a practical technique for capturing measurements was developed and demonstrated. A new set of test equipment was made using these finding. Subsequent results using this equipment were able to demonstrate that bioimpedance measurement could be taken from a limb while FES was being used, and that these measurement could be used as a feedback signal to control the FES to maintain a target limb position.

This work forms the basis of a novel approach to the control of FES that uses feedback from the user’s limb to determine the position of the limb in free space without need for additional sensors.

More information

Identifiers

Catalogue record

Export record