Systematik zur Beurteilung passiver Überkopf-Exoskelette

This thesis evaluates the influence of passive, industrial overhead exoskeletons on the physiology of the human body. In the highly automated automotive industry employees still must undergo considerable physical strain at certain workplaces. This includes jobs where employees are required to work at or above shoulder level. The resulting physical stress on the shoulder-arm system can promote the development of musculoskeletal disorders. Overhead exoskeletons are regarded as a cost-effective and quickly applicable individual ergonomic measure, although the resulting effects on the wearer have not yet been sufficiently researched. Existing studies are often limited to the application of individual measuring methods with the aim of recording and evaluating the stress on individual local body parts. Furthermore, most of these studies have been conducted in laboratory environments that do not adequately reflect real work conditions. Field studies that were conducted at real workplaces, especially those using objective measurement methods, are limited to an exceedingly small number.
The thesis sets in with the basics of work-related musculoskeletal diseases, which are typically found more often in the manufacturing industry. A connection between an increase in stress on the shoulder-arm-system, caused by working in the over-head posture, and the increased incidence of musculoskeletal diseases of the shoulder-arm-system is presented. In addition, an overview of the current methods of assessing strains and stresses will be given, and the research gap will be high-lighted through a comparison with existing studies. On this basis, the hypotheses are then derived. Within three study sections the whole body as well as the body part related stresses are evaluated subjectively and objectively. In the first study, the basic suitability of overhead exoskeletons as an ergonomic measure to reduce workplace-related stress is examined. Secondly a suitable measurement methodology to assess the physiological effects is developed. In the second study, the methodology will be applied in a comprehensive laboratory study, while in the second part of the study, the suitability of the measurement methodology will be tested in an explorative field study. In the third and last study section, two further field studies including three different overhead exoskeletons will be conducted, to check whether the results of the laboratory study can be transferred to the field.
The results of the work show a significant perceived reduction of the subjective stress in the upper arm, shoulder, and neck as well as in the whole body while using a passive overhead exoskeleton. However, increases in subjective stress in body areas where the loads are redistributed to are small. These findings are equally valid for all studies conducted, both under laboratory and field conditions. Using the developed measurement methodology, significant relative reductions of the electromyographic activity of the local shoulder and arm lifting muscles (Musc. trapezius pars descendens and deltoideus pars acromialis up to 40 %) as well as an in-crease of the local oxygen tissue saturation were detected under laboratory conditions. In contrast, the global stress parameters were only moderately influenced in the laboratory study. While absolute and specific oxygen uptake as well as the energy turnover showed small reductions (7.3 %, 5.1 % and 12.3 %) during dynamic movements, almost no influence, or just a minor increase (1.0 %, 7.7 % and 1.3 %) could be measured for different static postures. However, the intervention reduced the working pulse rate by about 21 % across all working postures. The results of the field studies at different workplaces showed that the global stress parameters are only marginally influenced using different overhead exoskeletons. Under laboratory conditions, the support effect of overhead exoskeletons is deliberately isolated, and reductions in objective global strain become measurable. Under real conditions, artificial isolation is not present and the postulated reduction effects are too small to be statistically significant.
The use of overhead exoskeletons as a measure to improve ergonomic conditions at the workplace requires a detailed and comprehensive investigation of the physiological impact. Based on the developed holistic approach, the thesis draws a first picture of the physiological consequences by using a standardized evaluation method that measures subjective and objective as well as local and global stress parameters. Further laboratory and field studies with larger populations and other exoskeletons should be carried out using the same developed measurement methodology to make accurate recommendations for the use in industrial environments.