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+# The Lumbar Spine Model
+
+The Lumbar spine contains **5 vertebrae** with 3 DoF spherical joints in
+between, **188 muscle fascicles** and a model of intra-abdominal pressure.
+
+```{raw} html
+<!--<img src="../_static/LumbarSpineBack.jpg" alt="Smiley face" width="32%">
+<img src="../_static/LumbarSpineFront.jpg" alt="Smiley face" width="32%">-->
+<video width="32%" style="display:block; margin: 0 auto;" controls autoplay loop>
+    <source src="../_static/LumbarSpine_rotating_model.mp4" type="video/mp4">
+Your browser does not support the video tag.
+</video>
+```
+
+Since it is impractical to measure or specify the motions of individual segments within the spine
+(termed functional spinal units or FSU), these motions are prescribed by default as a function of overall lumbar curvature.
+These functions are known as kinematic rhythms.
+
+Facet joints are also not employed by default, since most applications do not focus on the lumbar spine
+section. However, several examples in `AMMR/Applications` folder demonstrate possible mechanisms of
+facet joint incorporation and detailed modeling of the lumbar spine.
+
+The spinal muscles do not include the force-length-velocity relations (i.e.
+we use the so-called simple muscle model). The only input parameter in
+the muscle model is the cross-sectional area multiplied by a factor.
+Daggfeldt and Thorstensson (J.Biomech. 2003, 36: 815-825) didn't include
+the force-length-velocity relations either.
+
+The inclusion of the lumbar spine ligaments is optional and can be defined as a cumulative stiffness of
+FSUs or as separate elastic elements. Similarly, the intervertebral disc
+(IVD) stiffness can be defined as a single cumulative value for a FSU or as
+linear and nonlinear functions for the disc alone. This, however, is
+mostly utilized for the spine specific applications, where such a level of
+detail is important.
+
+In other cases, it has been shown that the torque
+production from ligaments might not be very important (Cholewicki and
+McGill, J.Biomech. 1992, 25: 17-28). The data of vertebrae dimensions
+and whole body parameters is taken from: Nissan and Gilad (J.Biomech.
+19: 753-758, 1986) and mechanical properties of ligaments were taken
+from: Pintar et al. (J.Biomech. 25(11): 1351-1356, 1992).
+
+The spine model contains a preliminary model of the Intra Abdominal
+pressure (IAP). In short the abdomen is modeled as constant volume, which,
+when squeezed from the side by the transversus muscles extends the spine
+by pushing on the rib thorax and the pelvic floor.
+
+From the mathematical
+point-of-view, this lets the abdominal muscles function as spine
+extensors, and they become part of the whole recruitment problem. The
+limit of the IAP was set to 26600 Pa, which was based on measurements on
+well-trained subjects (Essendrop, M., 2003. Significance of
+intra-abdominal pressure in work related trunk-loading. Ph.D. Thesis,
+National Institute of Occupational Health, Denmark.) and using
+geometric/anatomical estimates of pressure surface area and area
+centroids, which in turn determines the effective moment arm of the
+resulting forces.
+
+## Example Configuration
+
+The lumbar spine model is always part of the AnyBody Human model. The muscles can
+be enabled/disabled, and the lumbar disc stiffness can be controlled.
+
+:::{seealso}
+:class: margin
+The {doc}`Trunk configuration parameters <../bm_config/trunk>` for a
+full list of Trunk parameters.
+:::
+
+```AnyScriptDoc
+#define BM_TRUNK_MUSCLES ON
+#define BM_TRUNK_DISC_STIFNESS _DISC_STIFFNESS_LINEAR_
+```
+
+## Resources
+
+More details on the lumbar spine model can be found online:
+
+- Presentation about the [Abdominal pressure
+  Presentation](https://www.anybodytech.com/wp-content/uploads/publication_files/AbdominalPressureModel.pdf)
+- Webcast: [A lumbar spine model with facets joints and a dynamic stabilization device](https://www.anybodytech.com/download/a-lumbar-spine-model-with-facets-joints-and-a-dynamic-stabilization-device)
+- Webcast: [Implementation of facet joints in a lumbar spine model](https://www.anybodytech.com/download/implementation-of-facet-joints-in-a-lumbar-spine-model/)
+- Webcast [A detailed rigid-body cervical spine model based on inverse
+  dynamics](https://www.anybodytech.com/em_publication/a-detailed-rigid-body-cervical-spine-model-based-on-inverse-dynamics/)
+- Webcast [A generic detailed rigid-body lumbar spine model](https://www.anybodytech.com/em_publication/a-generic-detailed-rigid-body-lumbar-spine-model)
+- PowerPoint presentation [Spine Rhythm Presentation (PDF with videos click to activate
+  them)](https://www.anybodytech.com/wp-content/uploads/publication_files/Spinerhythm.pdf)
+
+You can read more about this lumbar spine model and some preliminary
+validation in the following article:
+
+- de Zee, M., L. Hansen, C. Wong, J. Rasmussen, and E.B. Simonsen. A
+  generic detailed rigid-body lumbar spine model. J.Biomech. 40:
+  1219-1227, 2007.
+
+## References
+
+- Andersson,E., Oddsson,L., Grundstrom,H.,Thorstensson,A., The role of
+  the psoas and iliacus muscles for stability and movement of the
+  lumbar spine, pelvis and hip, Scand. J. Med. Sci. Sports,5 (1995)
+  10-16.
+- Bogduk,N., Clinical anatomy of the lumbar spine and sacrum, Churchill
+  Livingstone, Edinburgh, 1997.
+- Bogduk,N., Macintosh,J.E., Pearcy,M.J., A universal model of the
+  lumbar back muscles in the upright position, Spine, 17 (1992)
+  897-913.
+- Bogduk,N., Pearcy,M.J., Hadfield,G., Anatomy and biomechanics of
+  psoas major, Clin. Biomech., 7 (1992) 109-119.
+- Daggfeldt,K., Thorstensson,A., The role of intraabdominal pressure in
+  spinal unloading, J. Biomech., 30 (1997) 1149-1155.
+- Daggfeldt,K., Thorstensson,A., The mechanics of back-extensor torque
+  production about the lumbar spine, J. Biomech., 36 (2003) 815-825.
+- Heylings,D.J.A., Supraspinous and interspinous ligaments of the human
+  lumbar spine, J. Anat., 125 (1978) 127-131.
+- Hodges,P.W., Cresswell,A.G., Daggfeldt,K., Thorstensson,A., In vivo
+  measurement of the effect of intra-abdominal pressure on the human
+  spine, J. Biomech., 34 (2001) 347-353.
+- Macintosh,J.E., Bogduk,N., The biomechanics of the lumbar multifidus,
+  Clin. Biomech., 1 (1986) 205-213.
+- Macintosh,J.E., Bogduk,N., 1987 Volvo award in basic science. The
+  morphology of the lumbar erector spinae, Spine, 12 (1987) 658-668.
+- Macintosh,J.E., Bogduk,N., The attachments of the lumbar erector
+  spinae, Spine, 16 (1991) 783-792.
+- Macintosh,J.E., Bogduk,N., Munro,R.R., The morphology of the human
+  lumbar multifidus, Clin. Biomech., 1 (1986) 196-204.
+- McGill,S.M., Norman,R.W., Effects of an anatomically detailed erector
+  spinae model on L4/L5 disc compression and shear, J. Biomech., 20
+  (1987) 591-600.
+- Pearcy,M.J., Bogduk,N., Instantaneous axes of rotation of the lumbar
+  intervertebral joints, Spine, 13 (1988) 1033-1041.
+- Penning,L., Psoas muscle and lumbar spine stability: a concept
+  uniting existing controversies. Critical review and hypothesis, Eur.
+  Spine J., 9 (2000) 577-585.
+- Prestar,F.J., Putz,R., Das Ligamentum longitudinale posterius -
+  morphologie und Funktion, Morphol. Med., 2 (1982) 181-189.
+- Prilutsky,B.I., Zatsiorsky,V.M., Optimizationbased models of muscle
+  coordination, Exerc. Sport Sci. Rev., 30 (2002) 32-38.
+- Stokes,I.A., Gardner-Morse,M., Lumbar spine maximum efforts and
+  muscle recruitment patterns predicted by a model with multijoint
+  muscles and joints with stiffness, J. Biomech., 28 (1995) 173-186.
+- Stokes,I.A., Gardner-Morse,M., Quantitative anatomy of the lumbar
+  musculature, J. Biomech., 32 (1999) 311-316.
+- Pintar et al., “Biomechanical properties of human lumbar spine
+  ligaments”, J Biomech, Vol. 25(11), 1992, pp.1351-1356.