Putting the Ergonomics into Chair Design
Office Chairs UK, 22/10/2014
Failing to consider ergonomics in the design of a chair is likely to lead to a poor user experience. For instance, a chair that does not provide sufficient support to the lower back can lead to back pain, which can result in anything from discomfort through to long-term sick leave. Many occupations today require individuals to be sat for most of their working day; it is therefore essential that ergonomics is central to the design of a chair.
Ergonomics is the scientific discipline that is concerned with understanding people and applying it to design, with the overall goal of optimising the design for human use. To achieve this, there is a need to adopt a User Centred Design approach, an approach that places the intended user at the centre of the design process. This approach requires the application of ergonomics theory, principles, data and methods to the design.
From a user-centred perspective, good design focuses on creating products that bring together three key principles; 1) functionality; 2) usability and 3) desirability. Functionality refers to the intended purpose of a product. In relation to a chair, this is to provide stable bodily posture that is comfortable over a period of time, physiologically supports the spine, and appropriate for the activity that is to be performed. In order to achieve these requirements there is a need to consult appropriate anthropometric data. Anthropometric data refers to the measurement of people in either a rigid posture (static data) or in motion (dynamic data). These measurements are then mapped to the chair in order to determine the appropriate dimensions for the various chair components. For instance, the measurement for hip-breath would be used to determine seat width; sitting elbow height would be used to determine the height of the armrests. Other seating dimensions determined from anthropometric data include, seat height and depth, backrest height and width, lumbar support height and protrusion, seat angel/tilt, armrest width, etc. To add complexity to this, humans vary greatly in size and in order to accommodate the range of human body sizes that exist within the target population there is a need to incorporate a level of adjustability within the design of the chair. The range of adjustability within a given seating dimension can also be derived from anthropometric data by considering the smallest dimensions for a given body measurement and the largest. Whilst anthropometric data sets provide one source of data there are also other methods things as fitting trials. This approach involves recruiting a large sample of users from the target population, measuring them, getting them to interact with a mock-up of the chair to determine the optimum sizing for it. Standards are also used on sizing guidance such as the BS EN 1335-1:2000, Office furniture – Office work chair – Part 1: Dimensions – Determination of dimensions.
The second principle of user-centred design is usability – this refers to designing products that are efficient, effective and satisfactory to use. In relation to chair design, there is a need to ensure that the product’s functionality (adjustability) is usable. A wide range of ergonomic tools and techniques can be employed to help achieve this, some of these include:
- Affordance - visual cues that help people to better understand how the chair is adjusted (e.g. use of icons for chair adjustment controls)
- Zone of convenient reach – positioning interactive features within a zone that can be comfortably reached from a sitting position
- Task analysis – can help identify any unnecessary steps that the user has to go through in order to achieve their desired seating position
- Enhancing accessibility - the contrast and size of visual characteristics can be increased to improve legibility, the shape and material of interactive characteristics can be modified to support gripping, the force required to operate functions can be reduced to ensure the product isn’t too demanding to use, particularly for users who may suffer from physical impairments etc.
Usability testing is often employed at this stage of development. Usability testing involves recruiting a sample of representative users and giving them tasks to perform with the product in a given scenario (e.g. ‘You have been given a new chair at work, adjust the seat height of the chair appropriate for you to work at your desk’). Users are observed completing these tasks and measures are taken such as time taken and the number of errors made when performing tasks along with feedback related to the user’s overall level of satisfaction, comfort and experience.
The third and final principle to consider when designing an ergonomic chair is desirability. This refers to the extent to which the product connects with the user on an emotional and/or hedonic level e.g. social impression, personal values, feeling of quality etc. It is therefore important to obtain a holistic understanding of your target user in order to achieve this. In particular, their values, how they want to feel when interacting or viewing the chair, what impression would they like to give off to others, etc. This type of understanding can be gathered through qualitative research methods from interviews through to design ethnography. Desirability testing can also be employed to ensure that the holistic understanding of the target user has been accurately translated into a set of appropriate chair characteristics.
Overall, it can be said that ergonomics plays a significant role in the design and development of chairs. It is in fact the discipline that is focussed towards ensuring the final design delivers value to its intended users. Failure to apply a User Centred Design approach to the design of chair (and in fact any product) is likely to result in a poor user experience, which can only lead to failure in the marketplace.