A comprehensive evaluation of human soft-tissue deformation during sitting

This research focuses on understanding the complex human-seat interaction. Scientific knowledge on buttock deformation is inadequate, though an appreciable amount of research has been executed in seat comfort & discomfort, seat vibrational behaviour, digital human modelling, postural ergonomics and seat dynamics. Specifically, this research explores soft tissue deformation in x, y and z axes, herein referred to as LM spread, AP spread and Compression respectively, using a motion capture system.

The buttock was divided into two regions around the Greater Trochanter body landmark separated by 40mm. The upper region was known as GT and the lower as GTX. Motion capture markers were placed around the GT and GTX buttock circumference in 150 increments from the side to rear. Seating trials were performed on a rigid seat at three angles – flat, 50 and 100. At each seat incline, three (3) forms of spread values for Compression, AP spread and LM spread were obtained, leading to a series of results in Chapters 4 – 6.

Each set of results comprised an array of hybrid marker values, which in turn were formed from shortlisted trial values. A series of correlation analysis were performed across all seat levels. Relationships/associations between buttock spread values were first established. Then, associations between anthropometric measurements and buttock spread values were identified. In Chapter 5, the results of the first study were validated and a further exploration was done between a rigid and cushioned seat. In Chapter 6, the results from both studies were combined to yield a larger dataset. This was done based on the statistical perspective that a larger sample size is more reliable, accurate and of a closer approximation to the actual population than either study’s sample.

In Chapter 7, several concepts were introduced with the aim of breaking down the general knowledge about buttock deformation into more specific knowledge about the spread attributes of clusters/segments of the population sample. In other words, a bid to understanding how buttock deformation varies between groups of people having similar spread attributes. The key findings are discussed within each chapter, but the salient points are converged in Chapter 8. It was found that some anthropometric measurements such as hip girth and % body fat do explain the variability in buttock deformation, and that varying seat angles also have an influence on soft tissue deformation.