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Reducing low-back disorders using a new sitting design.

NIOSH 2005 Jul; :1-67
Occupational low back pain (LBP) is alarmingly common, with a 100 million workdays lost in the United States each year. As the leading cause of disability in individuals less than 50 years old, LBP imposes a tremendous economic burden, with a direct treatment cost exceeding $25 billion in 1990 alone and the seated work tasks have a 25-76% prevalence of musculoskeletal discomfort. Although a number of occupational risk factors have been cited, the primary causes for work-related LBP include inappropriate curvature of the spine and pelvis induced by sitting, and sustained static muscle, ligament, and disc load caused by prolonged static sitting. Sitting induces backward rotation of the pelvis, reduction in lumbar lordosis, increased intervertebral disc pressure, tension in paraspinal muscles and ligaments in lumbar region, excessive pressure over the ischium and coccyx, and certainly the associated LBP. This project investigated a new sitting concept for office chair to determine its potential beneficial effects to working individuals with sitting related LBP. This new seating system features an enhanced backrest, which is adjustable both in height and shape, providing various degrees of lumbar support, and a split seat pan, in which the back part of seat (BPS) can be dynamically tilted down with respect to the front part of the seat (FPS), providing adjustment of thigh and ischial support. Along with this new seating concept, a new sitting posture, WO-BPS sitting posture, was proposed by the investigators, which stands for using the protruded lumbar support on the backrest together with the released ischial support on the seat. In this project, research was carried out not only through biomechanical and physiological test in laboratory and radiological imaging settings, but also through a 12-week subjective evaluation of the new office chair in practical working environment to collect feedbacks from individuals with sitting related low back complaints. Major findings from the project are: 1. The proposed novel sitting concept, which combines adjustable ischial load relief and lumbar support enhancement, effectively relieved LBP symptoms in the majority of the LBP patients who participated in the study; 2. The alleviation of the sitting related complaints, the improvement of sitting posture, and the beneficial sitting load redistribution, are achieved optimally by simultaneously using two interventions: the adjustable protruded lumbar support, and the tilted down back part of the seat to achieve ischial load release; 3. The alleviation of the LBP symptoms by using this sitting concept is attributed to the significant sitting posture correction effect, which results in significant increased lumbar intervertebral disc height, forward rotation of the sacrum, increased lumbar lordosis, and significantly decreased muscle effort of paraspinal muscles in lumbar region; 4. The alleviation of the LBP symptoms by using this sitting concept is attributed to the significant load redistribution between the seat and backrest, and between the posterior and the middle portion of the seat pan; 5. The study chair also helped effectively relieve buttock pain symptoms in the majority of the LBP participants; 6. Sitting in this study chair was found overall comfortable and significantly increase sitting tolerance in the majority of the participants; and, 7. The new sitting concept, WO-BPS sitting posture, provided by the study chair, was found preferred by the majority of the participants. In conclusion, the investigated new sitting concept has been confirmed to have significant postural correction effect to individuals with sitting related LBP; thus significantly reducing one of the primary causes of occupational LBP. The investigators believe that this is the first seating system which provides sitting posture adjustment and correction by the combination of adjusting protruded lumbar support and the reduced ischial load. Moreover, the posture adjustability and flexibility provided by the novel seating system offer ample options for the users to find the optimal sitting postural configuration which best fits each individual's needs. Therefore, the investigators believe that, by introducing an automatic posture adjustment mechanism into current seating system, this seating concept would be transformed into a dynamic seating device which would have promising potentials to prevent prolonged static sitting, the other primary occupational cause for sitting related LBP, in individuals with occupations requiring long term sitting. Encouraging findings on benefits of this seating concept on occupational LBP suggest further research and development effort be invested for improvement of the prototype and implementation of this new seating device in practical working space.
Biomechanics; Back-injuries; Muscles; Muscle-tension; Injuries; Office-workers; Workers; Biomedical-engineering; Posture; Muscle-contraction; Musculoskeletal-system; Musculoskeletal-system-disorders; Ergonomics
Rehabilitation Institute of Chicago, 345 E. Superior Street, Room 1406, Chicago, IL 60611
Publication Date
Document Type
Final Grant Report
Funding Amount
Funding Type
Fiscal Year
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Identifying No.
NIOSH Division
Priority Area
Disease and Injury: Low Back Disorders
Source Name
National Institute for Occupational Safety and Health
Performing Organization
Rehabilitation Institute Research Corporation