Keyboard design through physiological strain measurements.

The physiologically tolerable range of positions for the joints of the upper extremities have been investigated for typing tasks by recording the myoelectric activities of the involved muscles. For long-term typing tasks a split keyboard is recommended allocating a key field to each hand. The fields should be rotated against each other in the horizontal plane and inclined laterally.

[Tremor reaction to mental and emotional stress]. / Reaktionen des Krafttremors auf informatorisch-mentale und informatorisch-emotionale Belastungen.

Reactions of tremor before and after stress were registered with a new method. Reactions with informatory-mental stress (adding tests with increasing time pressure) can only be interpreted by considering performance. Reactions with informatory-emotional stress (University examination; tasks in a central TV control room) are task specific when tremor is inter-individually normalized.

[Bioelectrode jellies for long-term monitoring (author's transl)]. / Bewertung von Kontaktvermittlern für Bioelektroden bei Langzeituntersuchungen.

The properties of 18 electrode jellies were investigated: electrical conductivity, ionic content, pH, skin irritation, and skin impedance reduction with different skin preparations, motion artifact, electrochemical noise with different electrode material, susceptibility to drying, ease of handling, and cost. There were significant differences of performance. Skin compatibility after 8 h ranged from "no irritation" to "severely irritating". A skin irritation most likely occurred with decornifying skin preparation. The specific skin impedance 24 min after the application ranged from 15 k omega . cm2 to 125 k omega . cm2. The motion artifacts differed up to 250%. All jellies produced negligible noise with Ag/AgCl and stainless steel electrodes. However, with gold and silver electrodes the noise amounted to 19 and 23 mu V. The NaCl content was correlated to the skin irritation and the impedance reduction. The impedance reduction correlated inversely to the skin compatibility and the motion artifact. Guidelines for the selection of an appropriate jelly in ergonomic long-term monitoring are given.

[Approaches to reduce the retroaction of long-term monitoring of bioelectric events in ergonomic field studies (author's transl)]. / Rückwirkungsarme Ableitung bioelektrischer Signale bei arbeitswissenschaftlichen Langzeituntersuchungen am Arbeitsplatz.

When monitoring bioelectric signals the surface electrodes can cause a retroaction on the subject thereby introducing an error of measurement. There are two types of retroaction: physical and psycho-physiological. A physical retroaction due to the hydration process of the skin occurs if 'wet' electrodes are used for the recording of the skin conductance level (SCL) causing a continuous drift of the SCL and a decrease in sensitivity to SCL changes. Therefore a dry electrode was developed with improved performance: It exhibits less sensitivity to motion, is not subject to polarization, and features better SCL long-term stability. When recording the electrocardiogram or the electromyogram a psychophysiological retroaction occurs due to the annoyance caused by the skin-irritating abrading techniques in order to decrease the skin impedance and reduce the motion artifact. In an attempt to abandon the skin preparation whenever permissible without sacrificing the measurement accuracy a performance estimation procedure was developed. Basing on the information on the signal frequency content, the electrode contact area, the required accuracy of measurement and the amplifier input impedance a decision on the necessity of skin preparation is made. Moreover, the results of a study are reported investigating the reduction of motion artifacts by means of electrode design and appropriate electrode jelly formulation.

A model of bioelectrode motion artefact and reduction of artefact by amplifier input stage design.

Motion artefact voltages result from mechanical disturbances of bioelectrodes. For dry electrodes the effect of parameters related to the amplifier input stage on the artefact voltage is studied. The results indicate that the artefact voltage consists of two components termed delta R component and delta U component according to the motion-affected element. The delta R component is strongly dependent on the amplifier input resistance Rl and the input bias current lB. For negligible delta R artefacts Rl should be larger than 1 G omega and lB should be less than 50 pA when using bioelectrodes.

[Temperature dependent alterations of the surface-EMG and ECG: an investigation of the electrical transfer characteristics of the human skin (author's transl)]. / Temperaturabhängige Veränderungen des Oberflächen-EMG und EKG: Eine Untersuchung zum elektrischen Ubertragungsverhalten der menschlichen Haut.

The influence of local heating of the skin on the integrated EMG (registered with surface and subcutaneous electrodes), the amplitude of the ECG, the skin blood flow, the electrode impedance, the electrode-to-skin impedance, and the tissue impedance is investigated. Except for the increasing skin blood flow each of the variables exhibits a significant reduction with an increase in skin temperature. From these results the existence of two mechanisms is deduced mediating thermal influence on bioelectric signals picked up by surface electrodes: 1. An alteration of the signal source. 2. An alteration of the electric transfer characteristics of the tissue between signal source and electrode. Especially in quantitative surface electromyography the temperature dependence of the signal can be a source of error.

[Transfer characteristic of the motor system of the hand obtained by electrical stimulation and its bearing on force tremor (author's transl)]. / Ubertragungsverhalten des motorischen Systems der Hand bei elektrischer Anregung und seine Bedeutung für den Krafttremor

Pulse duration modulated signals were used to stimulate the extensor muscles of the hand. From this and from the isometric tension responses the frequency response of the human motor system was obtained. From the transfer characteristics of the components of the motor system which were taken from literature the frequency response of a closed-loop circuit model could be calculated. The theoretical frequency response was compared to the observed data. With increasing loop gain the model would show the characteristics of a filter tuned to the frequency of force-tremors.