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Technical Briefs

A Methodology for Quantifying Seated Lumbar Curvatures

[+] Author and Article Information
Samuel T. Leitkam

Department of Mechanical Engineering,  Michigan State University, East Lansing, MI 48824-1226leitkams@msu.edu

Tamara Reid Bush1

Department of Mechanical Engineering,  Michigan State University, East Lansing, MI 48824-1226reidtama@msu.edu

Mingfei Li

Department of Mathematical Sciences,  Bentley University, Waltham, MA 02452mli@bentley.edu

1

Corresponding author.

J Biomech Eng 133(11), 114502 (Nov 28, 2011) (6 pages) doi:10.1115/1.4005400 History: Received February 01, 2011; Revised October 26, 2011; Posted October 27, 2011; Published November 28, 2011; Online November 28, 2011

To understand the role seating plays in the support of posture and spinal articulation, it is necessary to study the interface between a human and the seat. However, a method to quantify lumbar curvature in commercially available unmodified seats does not currently exist. This work sought to determine if the lumbar curvature for normal ranges of seated posture could be documented by using body landmarks located on the anterior portion of the body. The development of such a methodology will allow researchers to evaluate spinal articulation of a seated subject while in standard, commercially available seats and chairs. Anterior measurements of boney landmarks were used to quantify the relative positions of the ribcage and pelvis while simultaneous posterior measurements were made of lumbar curvature. The relationship between the anterior and the posterior measures was compared. The predictive capacity of this approach was evaluated by determining linear and second-order regressions for each of the four postures across all subjects and conducting a leave-one-out cross validation. The relationships between the anterior and posterior measures were approximated by linear and second-order polynomial regressions (r2  = 0.829, 0.935 respectively) across all postures. The quantitative analysis showed that openness had a significant relationship with lumbar curvature, and a first-order regression was superior to a second-order regression. Average standard errors in the prediction were 5.9° for the maximum kyphotic posture, 9.9° for the comfortable posture, 12.8° for the straight and tall, and 22.2° for the maximum lordotic posture. These results show predictions of lumbar curvature are possible in seated postures by using a motion capture system and anterior measures. This method of lumbar curvature prediction shows potential for use in the assessment of seated spinal curvatures and the corresponding design of seating to accommodate those curvatures; however, additional inputs will be necessary to better predict the postures as lordosis is increased.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 4

Representative openness angle versus lumbar angle plot for a single subject with linear and second-order polynomial regression lines shown. The linear best-fit approximation is shown as a black line, while the second-order polynomial is shown as the gray curve. Smaller openness angles and lumbar angles indicate a more kyphotic posture while larger openness and lumbar angles indicate a more lordotic posture.

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Figure 3

Diagram of the openness angle, which was calculated from the coordinates identified with the hip joint center, anterior superior iliac spines, sternum and seventh cervical vertebra, and the lumbar angle as calculated from the coordinates identified with the mid-posterior superior iliac spines, twelfth thoracic vertebra, and most eccentric lumbar marker

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Figure 2

Subject seated in each of the four postures. From left to right: maximum kyphotic, comfortable, straight and tall, and maximum lordotic.

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Figure 1

Anterior and posterior marker placement on subjects as viewed in a seated position

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Figure 5

Openness angle versus lumbar angle for all subjects with linear regressions shown for each posture

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