The effect of perception of seat width on back-to-sit task.

[Purpose] The movement trajectory in daily motion is strongly associated with information regarding the properties of the environment. In the case of the back-to-sit task, it may vary according to chair property. The purpose of this study was to investigate whether trajectory formation in back-to-sit tasks by healthy adults depends on seat width information. [Participants and Methods] Ten healthy young males performed a back-to-sit task in 5 seat width conditions (80%, 90%, 100%, 110%, and 120% of each participant's buttock breadth). The motion analysis system and force plates were set at a sampling frequency of 250 Hz. The spatial and temporal variables were calculated to examine the effect of seat width. A questionnaire was also administered to examine whether the participants were aware of each seat width in comparison with their own buttock breadth as narrow or large. [Results] The questionnaire results showed that many participants were aware but some were unaware of the relative comparison of their size to the seat width. Nevertheless, the spatial and temporal variables were invariant under the different seat width conditions. [Conclusion] In healthy adults, the trajectory formation in back-to-sit tasks is not dependent on the perception of seat width information under their variability as per daily situations.

Chair Size Design Based on User Height.

General principles derived from anatomical studies of human body sizes should be applied to chair designs. Chairs can be designed for a specific user or a particular group of users. Universal chairs for public spaces should be comfortable for the largest possible group of users and should not be adjustable, such as office chairs. However, the fundamental problem is that the anthropometric data available in the literature either come from many years ago and are out of date or do not provide a complete set of all the dimensional parameters of a sitting human body position. This article proposes a way to design chair dimensions solely based on the height range of the intended chair users. For this purpose, based on literature data, the main structural dimensions of the chair were assigned to the appropriate anthropometric body measurements. Furthermore, calculated average body proportions for the adult population overcome the incompleteness, outdated and burdensome access to anthropometric data and link the main chair design dimensions to one easily accessible anthropometric parameter: human height. This is achieved by seven equations describing the dimensional relations between the chair's essential design dimensions and human height or even a height range. The result of the study is a method of determining the optimal functional dimensions of a chair for a chosen range of sizes of its future users based only on users' height range. Limitations of the presented method: the calculated body proportions are correct only for people with a standard body proportion characteristic of adults, i.e., they exclude children and adolescents up to 20 years of age, seniors, and people with a body mass index exceeding 30.