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Biomechanical effects of sitting with adjustable ischial and lumbar support on occupational low back pain: evaluation of sitting load and back muscle activity.

Makhsous M, Lin F, Bankard J, Hendrix RW, Hepler M, Press J - BMC Musculoskelet Disord (2009)

Bottom Line: The load and interface pressure on seat and the backrest, and back muscle activities associated with usual and this Off-Loading posture were recorded and compared between the two postures.It also significantly decreased the contact area on the seat and increased that on the backrest.These effects are similar in individuals with and without LBP.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physical Therapy and Human Movement Sciences, Northwestern University, Chicago, IL, USA. m-makhsous2@northwestern.edu

ABSTRACT

Background: Compared to standing posture, sitting decreases lumbar lordosis, increases low back muscle activity, disc pressure, and pressure on the ischium, which are associated with occupational LBP. A sitting device that reduces spinal load and low back muscle activities may help increase sitting comfort and reduce LBP risk. The objective of this study is to investigate the biomechanical effect of sitting with a reduced ischial support and an enhanced lumbar support (Off-Loading) on load, interface pressure and muscle activities.

Methods: A laboratory test in low back pain (LBP) and asymptomatic subjects was designed to test the biomechanical effect of using the Off-Loading sitting posture. The load and interface pressure on seat and the backrest, and back muscle activities associated with usual and this Off-Loading posture were recorded and compared between the two postures.

Results: Compared with Normal (sitting upright with full support of the seat and flat backrest) posture, sitting in Off-Loading posture significantly shifted the center of the force and the peak pressure on the seat anteriorly towards the thighs. It also significantly decreased the contact area on the seat and increased that on the backrest. It decreased the lumbar muscle activities significantly. These effects are similar in individuals with and without LBP.

Conclusion: Sitting with reduced ischial support and enhanced lumbar support resulted in reduced sitting load on the lumbar spine and reduced the lumbar muscular activity, which may potentially reduce sitting-related LBP.

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Related in: MedlinePlus

Experimental setup for laboratory test. The picture shows the actual experimental chair with Xsensor pressure mats on. It is shown in the Off-Loading configuration. The inset shows how the subject fit in the chair in an Off-Loading configuration, and the adjusting angle of the BPS.
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Figure 1: Experimental setup for laboratory test. The picture shows the actual experimental chair with Xsensor pressure mats on. It is shown in the Off-Loading configuration. The inset shows how the subject fit in the chair in an Off-Loading configuration, and the adjusting angle of the BPS.

Mentions: An instrumented laboratory chair representing the proposed sitting concept[31] was utilized (Figure 1). The seat pan included a back part of the seat (BPS) which allowed inferior tilt down to 20° with respect to the front part of the seat (FPS). An attached motor allowed movement of the BPS. The seat pan was adjustable in depth, height, and width, to accommodate for varying body sizes. Both tilt angle of the BPS and seat depth were accurately recorded. The backrest-seat pan angle was set at 100°, with the seat pan parallel to the floor. An air bladder, with its pressure monitored by sensors, was embedded in the backrest, providing lumbar support adjustment in terms of height and protrusion. Automatic inflation/deflation of the lumbar support was achieved through an air pump. The air pressure threshold for the lumbar support was set between 7–8 KPa to avoid soft tissue injury. A Programmable Logic Controller (Vision 120, Unitronics, Israel) was used to control the motor and air pump, allowing the experimental chair to assume the following 2 sitting postures:


Biomechanical effects of sitting with adjustable ischial and lumbar support on occupational low back pain: evaluation of sitting load and back muscle activity.

Makhsous M, Lin F, Bankard J, Hendrix RW, Hepler M, Press J - BMC Musculoskelet Disord (2009)

Experimental setup for laboratory test. The picture shows the actual experimental chair with Xsensor pressure mats on. It is shown in the Off-Loading configuration. The inset shows how the subject fit in the chair in an Off-Loading configuration, and the adjusting angle of the BPS.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2654542&req=5

Figure 1: Experimental setup for laboratory test. The picture shows the actual experimental chair with Xsensor pressure mats on. It is shown in the Off-Loading configuration. The inset shows how the subject fit in the chair in an Off-Loading configuration, and the adjusting angle of the BPS.
Mentions: An instrumented laboratory chair representing the proposed sitting concept[31] was utilized (Figure 1). The seat pan included a back part of the seat (BPS) which allowed inferior tilt down to 20° with respect to the front part of the seat (FPS). An attached motor allowed movement of the BPS. The seat pan was adjustable in depth, height, and width, to accommodate for varying body sizes. Both tilt angle of the BPS and seat depth were accurately recorded. The backrest-seat pan angle was set at 100°, with the seat pan parallel to the floor. An air bladder, with its pressure monitored by sensors, was embedded in the backrest, providing lumbar support adjustment in terms of height and protrusion. Automatic inflation/deflation of the lumbar support was achieved through an air pump. The air pressure threshold for the lumbar support was set between 7–8 KPa to avoid soft tissue injury. A Programmable Logic Controller (Vision 120, Unitronics, Israel) was used to control the motor and air pump, allowing the experimental chair to assume the following 2 sitting postures:

Bottom Line: The load and interface pressure on seat and the backrest, and back muscle activities associated with usual and this Off-Loading posture were recorded and compared between the two postures.It also significantly decreased the contact area on the seat and increased that on the backrest.These effects are similar in individuals with and without LBP.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physical Therapy and Human Movement Sciences, Northwestern University, Chicago, IL, USA. m-makhsous2@northwestern.edu

ABSTRACT

Background: Compared to standing posture, sitting decreases lumbar lordosis, increases low back muscle activity, disc pressure, and pressure on the ischium, which are associated with occupational LBP. A sitting device that reduces spinal load and low back muscle activities may help increase sitting comfort and reduce LBP risk. The objective of this study is to investigate the biomechanical effect of sitting with a reduced ischial support and an enhanced lumbar support (Off-Loading) on load, interface pressure and muscle activities.

Methods: A laboratory test in low back pain (LBP) and asymptomatic subjects was designed to test the biomechanical effect of using the Off-Loading sitting posture. The load and interface pressure on seat and the backrest, and back muscle activities associated with usual and this Off-Loading posture were recorded and compared between the two postures.

Results: Compared with Normal (sitting upright with full support of the seat and flat backrest) posture, sitting in Off-Loading posture significantly shifted the center of the force and the peak pressure on the seat anteriorly towards the thighs. It also significantly decreased the contact area on the seat and increased that on the backrest. It decreased the lumbar muscle activities significantly. These effects are similar in individuals with and without LBP.

Conclusion: Sitting with reduced ischial support and enhanced lumbar support resulted in reduced sitting load on the lumbar spine and reduced the lumbar muscular activity, which may potentially reduce sitting-related LBP.

Show MeSH
Related in: MedlinePlus