Men and Women Sit on Different Planes

Preliminary in-house research by Keilhauer suggested that these two frequently observed postural variations – perch- ing and reclining – are gender-related. When users sit the way their bodies tell them to – as opposed to the way the ergonomics manuals tell them to – we noted a significant dif- ference in the intuitive positions assumed by men and those assumed by women.

Keilhauer contracted with Dr. Jack Callaghan, an expert in spine biomechanics at the University of Waterloo, Canada, to do an independent study of this phenomenon. Over the course of eight months, Dr. Callaghan and his research team collected data comparing postural alignment, body positioning, kinematics, center of mass, and seat pan inter- face pressure for male and female subjects.

The findings showed significant differences between genders in postural alignment and seating position on the chair. Con- tinuous spine and pelvic measures taken during the study re- vealed that females sat with a more anteriorly rotated pelvis and less lumbar and trunk flexion than males, who sat with a posteriorly rotated pelvis, greater lumbar flexion, and more forward-leaning trunk postures (Callaghan and Dunk, 2005).

These gender-related differences in pelvic rotation have sig- nificant implications for the design of task chairs that sup- port men and women equally. Differences in center of mass and positioning on the seat pan must be taken into account when designing a chair and mechanism that accommodate a woman’s more anteriorly positioned center of mass, and a backrest that allows her to sit deeply enough into the seat to get the benefit of lumbar support.

For males, whose posteriorly rotated pelvic position pre- disposes them to a more reclined postural alignment when performing seated office work, thoracic support may aid
in reducing the forward bending of the thoracic spine that results from sustained forward bending of the neck (Fitz- simmons, 2004).

Additional research by Dr. Jack Callaghan for Keilhauer found that a backrest design with thoracic support had a positive effect on the lumbar posture of males performing typing-related tasks (Callaghan, 2006).