Objective firmness, average pressure and subjective perception in mattresses for the elderly.
For elderly people, the desirable situation of living independently means facing everyday tasks and risks alone [Monk et al., 2006. Towards a practical framework for managing the risks of selecting technology to support independent living. Appl. Ergon. 37, 599-606]. One such task is buying a mattress through the same channels as younger people. Quite short trials (if any) in the store are usually the only basis for choice. Despite the long-term effects a mattress may have on the user, acceptance or rejection largely depends on this extremely short trial experience. This paper aims to cover the salient mechanical aspects of comfort and usability (rolling, getting up). The results should help manufacturers to know if the long-term benefits of their products are perceived in the short term by senior citizen customers. Four mattresses for the elderly chosen from a sample of 17 available on the Spanish market were compared in pairs for short-term effects (1 min pressure with both hands, 1 min sitting, 1 min lying on back, and 1 min lying on side), simulating a store purchasing trial by a group of young and elderly people in terms of differences between perceived firmness, usability (ease of movement) and comfort. The results of these comparisons were correlated to differences in objective properties such as pressure distribution and objective firmness. No differences in perception were found between young and old users. Only two of the four test methods for perceiving mattress firmness were necessary to explain the majority of variance: pressing the surface of the mattress with a part of the body (both hands or buttocks), and contact using the entire body (lying on back or side). A number of significant relationships were found, with the following of note: increments in 'objective firmness' (estimated from test load/deflection) correlate positively to increments in 'perceived firmness'; increments in 'average pressure' (measured using a mannequin) correlate positively to increments (within certain limits) in 'perceived firmness'; increments in 'objective firmness' and in 'average pressure' are associated with increments in 'overall comfort' and with reductions in 'difficulty in rolling". Finally, it was found that people with a higher body mass index tend to be (weak correlation) more sensitive to changes in 'objective firmness'.