A methodology to determine the optimum seat depth

Even though the seat pan carries most of the weight during sitting, the number of studies investigating the different aspects of the sitting area are limited. Seat depth has been based on anthropometry or the so-called industry practice. The relevance of the widely used seat depth measure is thus questionable. A methodology has been developed to evaluate the useful seat depth for a target population. The methodology is found to be reliable and valid based on both objective and subjective measurements. A chair with an 'adjustable' seat depth was designed and developed for this purpose. A total of 30 Chinese students were tested. The objective measure was the seat edge protrusion when seated. Eight seat features were rated using a 5-point scale. The results show that the seat depth's of 30.4 and 38cm are significantly different, with the seat depth of 38cm being on the 'long side'. In addition, the objective measure of seat edge protrusion indicated that a seat depth of 31-33cm is adequate for the South China region Chinese population. Based on the subjective ratings and the objective measure developed, it may be concluded that a seat depth of 31-33cm is appropriate for the same population. Relevance to industry - Anthropometry alone is not sufficient for the design of seats. The differing sensitivity in the buttock and thigh areas is an indication that chairs should be designed and selected depending on the population under consideration. The need for having chairs of variable depth has to be recognized especially during long periods of sitting.