title: Effective rocker shapes used by able-bodied persons for walking and fore-aft swaying: implications for design of ankle-foot prostheses.
abstract: The use of rocker models to understand functional tasks of the human lower limb is attractive because of their simplicity. Recent studies have determined a consistent feature of able-bodied walking termed the roll-over shape (ROS), which is the effective rocker shape that the lower limb system conforms to between initial contact and contralateral initial contact during walking. However, it is unclear what effective rocker shapes are used for fore-aft swaying. A better understanding of these shapes could be used to develop improved prostheses for this task, perhaps improving balance and balance confidence, and reducing the occurrence of falling in lower limb prosthesis users. We measured effective rocker shapes used by 11 able-bodied persons during walking and fore-aft swaying. We hypothesized that the curvature of the swaying shapes would be smaller (radius larger) than that of the walking shapes, providing a more stable interface with the ground during swaying. The radius (measured as the inverse of the curvature of the shape) was found to be about 1/3 of the leg length for walking, but over two times the leg length for swaying. A model examining the effective ankle stiffness necessary to achieve these curvatures suggests that the stiffness of a biomimetic prosthetic ankle would need to be over three times higher for fore-aft swaying than for walking. These results suggest that two separate modes would be needed in an ankle-foot prosthesis to mimic the physiologic system for walking and swaying.
authors.affiliation: Minneapolis VA Medical Center, Minneapolis, MN, USA. Andrew.Hansen2@va.gov
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Hansen
authors.forename: Charles C
authors.initials: CC
authors.lastname: Wang
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology*; D001696:Biomechanical Phenomena; D005260:Female; D005528:Foot / Q000502:physiology*; D006801:Humans; D007595:Joint Prosthesis; D008297:Male; D008953:Models, Anatomic; D004856:Postural Balance / Q000502:physiology*; D011474:Prosthesis Design; D016059:Range of Motion, Articular / Q000502:physiology; D012775:Shoes; D016138:Walking / Q000502:physiology*
references.citation: J Neurophysiol. 1996 Jun;75(6):2334-43
references.pmid: 8793746
references.citation: Prosthet Orthot Int. 2006 Dec;30(3):286-99
references.pmid: 17162519
references.citation: J Bone Joint Surg Am. 1979 Jul;61(5):756-9
references.pmid: 457719
references.citation: Prosthet Orthot Int. 2003 Aug;27(2):89-99
references.pmid: 14571938
references.citation: J Biomech. 2009 Aug 7;42(11):1746-53
references.pmid: 19446814
references.citation: J Rehabil Res Dev. 2007;44(1):11-20
references.pmid: 17551854
references.citation: J Rehabil Res Dev. 2005 May-Jun;42(3):381-90
references.pmid: 16187250
references.citation: J Rehabil Res Dev. 2004 Jul;41(4):547-54
references.pmid: 15558383
references.citation: Clin Biomech (Bristol, Avon). 2004 May;19(4):407-14
references.pmid: 15109762
references.citation: J Exp Biol. 2006 Oct;209(Pt 20):3953-63
references.pmid: 17023589
references.citation: Arch Phys Med Rehabil. 2001 Sep;82(9):1238-44
references.pmid: 11552197
references.citation: Arch Phys Med Rehabil. 2001 Aug;82(8):1031-7
references.pmid: 11494181
references.citation: J Orthop Res. 1990 May;8(3):383-92
references.pmid: 2324857
references.citation: Med Confl Surviv. 2004 Oct-Dec;20(4):294-306
references.pmid: 15688881