This report describes the work with refinement of the Ergo-Index model, initially developed in the 1980’s by a group of researchers and practitioners. Ergo-Index is intended to enable comparison of different methods to perform a work task with the aim to support the choice of working methods to satisfy ergonomics requirements as well as requirements on time consumption and production economics. The outputs from the method are assessments of recovery need, production time and load level. The project has been carried out in two parts, of which this report deals with the second part.
The objective has been to gain relevant information and to develop the Ergo-Index model further, especially regarding recovery, based on a literature review and an experimental study. In the experimental study maximum exerted forces as well as subjectively assessed Endurance and Resumption times for 15 different loading cases were determined with different load levels and loading times.
The results revealed a previously unknown fatigue-load phenomenon, namely that the recovery need was found to be shortest, expressed in relative loading time, for a medium load level (30 % of max), compared to low (10 % of max) and high (50 % of max) load levels. This led to some unexpected difficulties in the project.
After several rounds of modeling relations for endurance and recovery need, the new Ergo-Index was developed. This, partly performed by deriving at mathematical relationships via regression analysis and partly by using results from other published studies and also Swedish physical ergonomics legislation recommendations, is described in the report. Seven examples of applications of the model are also given. These form a start of a planned database where applied examples are gathered to facilitate the use of the method. These tasks were also evaluated with subjective methods by the participants, using Borg’s CR10 scale, a body map and interviews and photo- and video-documented.
The new model should to be applied and evaluated more than has been done up until now, before it is spread to a large extent. Application and evaluation is planned with a couple of companies.
The experimental results have also been used for developing a prediction model of perceived fatigue. Further, also based on the experimental study, where the working task was carried out with one repetition in two subsequent trials, a model for accumulation of fatigue is presented. Both these parts have not been tested or evaluated, but it is suggested to evaluate them in studies with applied repetitive working tasks. These results may also be used to form an enhanced recovery assessment model on occupational tasks for selection of working methods and job design from ergonomics and time perspectives for repetitive work.
Issues regarding modeling, such as field of application and accuracy, are discussed. Dissemination of the results, to companies, in educations as well as in the research community, is also described.
Stockholm, 2012. , vi, 43 p.