An appropriately contoured lumbar support is widely regarded as an essential component of a comfortable auto seat. Laboratory experiments have demonstrated that lumbar intervertebral disc pressure is lower when the spine is in an extended posture (lordosis) than when the spine profile is flat. These findings have led researchers to recommend longitudinally convex seatback contours that are intended to maintain or induce lordosis in the lumbar spine. In the present study, laboratory experiments were conducted to investigate the effects of changes in seatback contour on driver posture. The primary goal of the research was to identify preferred driving postures for a range of seatback contours. Preferred postures were examined to determine if drivers respond to longitudinally convex lumbar supports in auto seats by sitting with lumbar lodosis. In the first part of the study, 48 male and female subjects from 4 stature/gender groups operated an interactive laboratory driving simulator for 3 1-hr sessions with the lumbar support of a test seat adjusted to produce prominences of 0, 10, and 25 mm, respectively. Prior to each session, the standing posture of the subject was recorded. Posture and subject back contour data were collected by means of a sonic digitizing system. Changes in posture over the 1-hr simulations were found to be small. Based on the results from the first phase of testing, a second phase was conducted using short-duration sitting sessions to measure driver posture over a wider range of lumbar-support prominences. Eight subjects from each of the 4 stature/gender groups in the original pool of 48 subjects were recruited. Postures were measured after a 2-min driving simulation with lumbar-support prominences of 0, 25, 35, and 45 mm. Sessions were conducted in which the subject could adjust the vertical position of the support as well as with the support fixed. Posture was also measured in sessions for which the subject's sitting procedure was prescribed to maximize the subject's lumbar lordosis in a manner similar to that used in previous studies of the effects of lumbar support. Increasing the prominence of the lumbar support from 0 to 45 mm changed sitter-selected postures only slightly. Subject postures in sessions with the prescribed sitting procedure showed significantly more lumbar lordosis than in the preferred-posture conditions, indicating that the test conditions did not preclude postures with greater lordosis. Even when the sitting procedure was prescribed to maximize lordosis, the change in lumbar spine curvature with an increase in lumbar-support prominence was smaller than expected. These findings indicate that relatively large changes in the longitudinal contour of an automobile seat backrest do not result in similar changes in subject spine curvature. An analysis of changes in pelvis angle and leg posture with varying lumbar-support prominence and sitting procedure suggests that the extended-knee posture required with the typical automobile seat heights and pedal locations are key factors that prevent substantially lordotic postures.

  • Supplemental Notes:
    • This research was sponsored by Lear Seating Corporation, 21557 Telegraph Road, Southfield, MI 48034.
  • Corporate Authors:

    University of Michigan Transportation Research Institute

    2901 Baxter Road
    Ann Arbor, MI  United States  48109-2150
  • Authors:
    • Reed, Matthew P
    • Schneider, L W
    • Eby, BAH
  • Publication Date: 1995-3-31


  • English

Media Info

  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 130 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00724908
  • Record Type: Publication
  • Source Agency: National Highway Traffic Safety Administration
  • Report/Paper Numbers: UMTRI-95-12, HS-042 180
  • Contract Numbers: 391363
  • Files: HSL, TRIS, USDOT
  • Created Date: Aug 20 1996 12:00AM