As the pelvis rotates, the tissue on the buttocks is placed in shear load, or a scrubbing frictional motion, that is one of the primary causes of pressure sores while seated. When seat cushions seem too firm to an older person, they will often build up the surface with soft materials such as pillows, blankets, and towels. This is usually ineffective because the problem lies in the lack of seat suspension. New elasticized webbing materials used as seat springs and medium density foams used as cushioning materials will alleviate this problem. Another difficulty in chair design and manufacturing is accommodating the wide variation of body sizes and seated angle preferences among male and female elderly people.
Men generally prefer more recline in the back angle of a chair than do women.
The difference can be as great as 114 degrees from the horizontal plane for men and 103 degrees for women. The difference in feeling from variation in back angle is significant and variations in preferences are strongly held among men and women. Based on average body dimensions, the standard dimension for seat depth from the leading edge of the seat cushion to the seat back is 17 inches. The height of the cushion off the floor is recommended at 17 inches. Many adults are not accommodated by these standards.