Sitting Biomechanics Part I: Review of the Literature

Authors

• Donald D. Harrison, DC, PhD
  
• Sanghak O. Harrison, DC
• Arthur C. Croft, DC
• Deed E. Harrison, DC
• Stephan J. Troyanovich, DC

Publication

Journal of Manipulative and Physiological Therapeutics. November/December 1999; 22(9): 594-609.

Article Link

Sitting Biomechanics Part I: Review of the Literature

Abstract

Objective: To develop a new sitting spinal model and an optimal driver’s seat by using review of the literature of seated positions of the head, spine, pelvis, and lower extremities.
Data Selection: Searches included MEDLINE for scientific journals, engineering standards, and textbooks. Key terms included sitting ergonomics, sitting posture, spine model, seat design, sitting lordosis, sitting electromyography, seated vibration, and sitting and biomechanics.
Data Synthesis: In part I, papers were selected if (1) they contained a first occurrence of a sitting topic, (2) were reviews of the literature, (3) corrected errors in previous studies, or (4) had improved study designs compared with previous papers. In part II, we separated information pertaining to sitting dynamics and drivers of automobiles from part I.
Results: Sitting causes the pelvis to rotate backward and causes reduction in lumbar lordosis, trunk-thigh angle, and knee angle and an increase in muscle effort and disc pressure. Seated posture is affected by seat-back angle, seat-bottom angle and foam density, height above floor, and presence of armrests.
Conclusion : The configuration of the spine, postural position, and weight transfer is different in the 3 types of sitting: anterior, middle, and posterior. Lumbar lordosis is affected by the trunk-thigh angle and the knee angle. Subjects in seats with backrest inclinations of 110 to 130 degrees, with concomitant lumbar support, have the lowest disc pressures and lowest electromyography recordings from spinal muscles. A seat-bottom posterior inclination of 5 degrees and armrests can further reduce lumbar disc pressures and electromyography readings while seated. To reduce forward translated head postures, a seat-back inclination of 110 degrees is preferable over higher inclinations. Work objects, such as video monitors, are optimum at eye level. Forward-tilting, seat-bottom inclines can increase lordosis, but subjects give high comfort ratings to adjustable chairs, which allow changes in position. (J Manipulative Physiol Ther 1999;22:594-609)