Manual material handling still plays an important role in assembly work as well as in the service industry. By means of an ergonomic layout of working places, the effects of disadvantageous working conditions, especially static load resulting from unfavourable postures of the body as well as unnecessary physiological cost arising from body movements may be avoided. In this context knowledge about the optimum directions of horizontal arm movements is fundamental. Therefore by means of advanced methods of multi-channel electromyography (EMG) and applying computer assisted evaluation methods, physiological responses to one-handed horizontal material handling in a sitting position were recorded. In order to obtain myoelectric signals from the most important task-relevant muscles out of more than 40 muscle groups of the hand-arm-shoulder-system, preceding research was done also aiming at standardized lead positions for surface EMG. Groups of five young females each participated in a series of successive experiments, in which the direction of movements of the left arm was varied. The subjects worked without and with an external load imposed by weights of 0, 1, 2 and 4 kg. The movements between 20 degrees and 230 degrees--measured from the frontal plane of the subjects--included working from ahead and from behind. The lifting distance was 38 cm starting from different outward points within the reach to a fixed point near the body. Also in one test series the handling frequency was varied between 12, 24 and 48 lifts per minute. Assessment of the physiological cost by electromyographic activities (EA), especially the determination of the most stressful and least expensive directions of repetitive horizontal movements, was more effective when differentiating static and dynamic portions of muscular strain than common means of EA.
Manufacturers of ergonomic split keyboards promise maximum effcctivcness and comfort as well as a reduction of physical complaints. Jn order to determine the claimed positive effects, 10 male subjects (Ss) participated in standardized working tests during which they entered text into a PC> altcmatingly using a conventional keyboard and the test keyboard. Electromyographic activity (EA) of 8 muscle groups was simultaneously recorded during altogether 6 working phases with a duration of 10 min, each. Measurements of the maximum activity EA,,, via maximum voluntary contractions of the 8 muscJcs-which were necessary for calculating standardized electromyographic activity (SEA) used to represent muscle strain as a percentage-were always taken at the end of the experiment. Muscle strain varied from muscle to muscle but the level of the SEAvalues for the different muscles was reproducible and stable. Also, activation of most muscles acting on the shoulder, upper arm, forearm, and the hand showed differences which, though small in amount, could be statistically sccured and associated with the keyboard type. The ergonomic design of the tested keyboard led to objectively vcrifiablc and plausible reductions of muscle strain.
Knowledge about practicable methods of appropriate recording and processing of myoelectric data which has been accumulated and further developed during the last decade has been fed into a program system. The sane is true for 8 set of already carried-out and published investigations into the ergonomic evaluation of keyboards, armrests, and wrist rests as well as various hand-held tools. Making use of the specifically developed and well-proven sofhvare packages which can be loaded into ahnost all PCs for recording, analyzing, and standardizing electromyographic data, even a user who until now was less familiar with these tasks gains access to clectromyography as an efficient and important ergonomic method applicable with reasonable expenditure both in the laboratory and in the field.
Firefighters are subject to high physical and psychological stress and fire fighting often requires mastering complicated tasks under adverse conditions. In this job, the handling of the hose/nozzle combination is a central and often performed task. The objective of this field study was to ergonomically evaluate different designs of 3 fire nozzles – a multi-purpose nozzle according to a German standard, a pistol nozzle (AWG), and a supposedly ergonomic nozzle (Quadrafog) – with respect to the muscle strain associated with performing standardized working tests. Eleven firefighters (10 males and 1 female, aged 27–54) used the 3 nozzles in the practice area of a fire station. For 3 different working tasks (straight stream, wide fog, and alternating operation), electromyographic activity was monitored continuously from 7 muscles of the right and left hand-arm-shoulder system using a PC-based mobile data registration system. Specially developed questionnaires provided subjective assessments of the ergonomic quality of the fire nozzles. The standard nozzle – which is still very frequently used – is only suited for "water go" for extended periods of time, but not for dynamic work. Especially the nozzle operator's arm musculature is subjected to high strain by the hose forces, which depend on water pressure and flow. AWG and Quadrafog led to substantially lower overall strain and smaller static components. Only in pure straight stream fire fighting was there no difference between the standard nozzle and the other models. High static portions characterize straight stream as well as wide fog operation. Both operations required small movements of the body so that the static portions became more noticeable. Overall, the AWG fire nozzle exhibited the most balanced strain profile with non-critical static values and a tolerable overall strain for alternating operations. These results are in accordance with the fire fighters' subjective preference for this model. It is unfortunate that currently the sole focus remains still on the price rather than the usability, which determines the physiological costs that must be paid by the operator. In the future, more attention should be paid to the compatibility between the characteristics of the human organism and the technical components of the tool.
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