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Research Papers

Use of Kinetic and Kinematic Data to Evaluate Load Transfer as a Mechanism for Flexion Relaxation in the Lumbar Spine

[+] Author and Article Information
Samuel J. Howarth

Associate Professor
McMorland Family Research
Chair in Mechanobiology
Department of Graduate Education and
Research Programs,
Canadian Memorial Chiropractic College,
Toronto, ON M2H 3J1, Canada
e-mail: showarth@cmcc.ca

Paul Mastragostino

Canadian Memorial Chiropractic College,
Toronto, ON M2H 3J1, Canada
e-mail: pmastragostino@cmcc.ca

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received February 19, 2013; final manuscript received July 2, 2013; accepted manuscript posted July 29, 2013; published online September 13, 2013. Assoc. Editor: Brian D. Stemper.

J Biomech Eng 135(10), 101004 (Sep 13, 2013) (6 pages) Paper No: BIO-13-1088; doi: 10.1115/1.4025112 History: Received February 19, 2013; Revised July 02, 2013; Accepted July 04, 2013

Flexion relaxation (FR) in the low back occurs when load is transferred from the spine's extensor musculature to its passive structures. This study investigated the influence of added upper body mass on low back kinetics and kinematics at the FR onset. Sixteen participants (eight male, eight female) performed standing full forward spine flexion with 0%, 15%, and 30% of their estimated upper body mass added to their shoulders. Electromyographic data were obtained from the lumbar erector spinae. Ground reaction forces and kinematic data from the lower limbs, pelvis, and spine were recorded. Extensor reaction moments (determined using a bottom-up linked segment model) and flexion angles at the FR onset were documented along with the maximum spine flexion. The angle at the FR onset increased significantly with added mass (p < 0.05). Expressing the FR onset angle as a percent of the full range of trunk flexion motion for that condition negated any differences between the added mass conditions. These findings demonstrate that low back kinetics play a role in mediating FR in the lumbar spine.

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Figures

Grahic Jump Location
Fig. 1

Experimental setup used in this study and screen capture of Visual 3D animation

Grahic Jump Location
Fig. 2

Sample data illustrating a linear envelope of the electromyographic data recorded from the lumbar erector spinae (solid black line), the flexion angle time history (solid gray line), and the extensor reaction moment time history (dashed gray line). The myoelectric onset of flexion relaxation in the lumbar erector spinae is also included along with the maximum lumbar flexion angle.

Grahic Jump Location
Fig. 3

Graphical representations combining kinetic and kinematic data obtained at the onset of flexion relaxation for both (a) males and (b) females. Data reported by Dolan et al. [16] for the spine flexion angle versus low back passive extensor moment relationship are also presented for a qualitative comparison. Error bars represent the standard error of the mean.

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