Controlling propulsive forces in gait initiation in transfemoral amputees. (bibtex)
by Helco G. van Keeken, Aline H. Vrieling, At L. Hof, Jan P K. Halbertsma, Tanneke Schoppen, Klaas Postema, Bert Otten
Abstract:
During prosthetic gait initiation, transfemoral (TF) amputees control the spatial and temporal parameters that modulate the propulsive forces, the positions of the center of pressure (CoP), and the center of mass (CoM). Whether their sound leg or the prosthetic leg is leading, the TF amputees reach the same end velocity. We wondered how the CoM velocity build up is influenced by the differences in propulsive components in the legs and how the trajectory of the CoP differs from the CoP trajectory in able bodied (AB) subjects. Seven TF subjects and eight AB subjects were tested on a force plate and on an 8 m long walkway. On the force plate, they initiated gait two times with their sound leg and two times with their prosthetic leg. Force measurement data were used to calculate the CoM velocity curves in horizontal and vertical directions. Gait initiated on the walkway was used to determine the leg preference. We hypothesized that because of the differences in propulsive components, the motions of the CoP and the CoM have to be different, as ankle muscles are used to help generate horizontal ground reaction force components. Also, due to the absence of an active ankle function in the prosthetic leg, the vertical CoM velocity during gait initiation may be different when leading with the prosthetic leg compared to when leading with the sound leg. The data showed that whether the TF subjects initiated a gait with their prosthetic leg or with their sound leg, their horizontal end velocity was equal. The subjects compensated the loss of propulsive force under the prosthesis with the sound leg, both when the prosthetic leg was leading and when the sound leg was leading. In the vertical CoM velocity, a tendency for differences between the two conditions was found. When initiating gait with the sound leg, the downward vertical CoM velocity at the end of the gait initiation was higher compared to when leading with the prosthetic leg. Our subjects used a gait initiation strategy that depended mainly on the active ankle function of the sound leg; therefore, they changed the relative durations of the gait initiation anticipatory postural adjustment phase and the step execution phase. Both legs were controlled in one single system of gait propulsion. The shape of the CoP trajectories, the applied forces, and the CoM velocity curves are described in this paper.
Reference:
Controlling propulsive forces in gait initiation in transfemoral amputees. (Helco G. van Keeken, Aline H. Vrieling, At L. Hof, Jan P K. Halbertsma, Tanneke Schoppen, Klaas Postema, Bert Otten), In J Biomech Eng, volume 130, 2008.
Bibtex Entry:
@ARTICLE{2008,
  author = {{van Keeken}, Helco G. and Vrieling, Aline H. and Hof, At L. and
	Halbertsma, Jan P K. and Schoppen, Tanneke and Postema, Klaas and
	Otten, Bert},
  title = {Controlling propulsive forces in gait initiation in transfemoral
	amputees.},
  journal = {J Biomech Eng},
  year = {2008},
  volume = {130},
  pages = {011002},
  number = {1},
  month = {Feb},
  abstract = {During prosthetic gait initiation, transfemoral (TF) amputees control
	the spatial and temporal parameters that modulate the propulsive
	forces, the positions of the center of pressure (CoP), and the center
	of mass (CoM). Whether their sound leg or the prosthetic leg is leading,
	the TF amputees reach the same end velocity. We wondered how the
	CoM velocity build up is influenced by the differences in propulsive
	components in the legs and how the trajectory of the CoP differs
	from the CoP trajectory in able bodied (AB) subjects. Seven TF subjects
	and eight AB subjects were tested on a force plate and on an 8 m
	long walkway. On the force plate, they initiated gait two times with
	their sound leg and two times with their prosthetic leg. Force measurement
	data were used to calculate the CoM velocity curves in horizontal
	and vertical directions. Gait initiated on the walkway was used to
	determine the leg preference. We hypothesized that because of the
	differences in propulsive components, the motions of the CoP and
	the CoM have to be different, as ankle muscles are used to help generate
	horizontal ground reaction force components. Also, due to the absence
	of an active ankle function in the prosthetic leg, the vertical CoM
	velocity during gait initiation may be different when leading with
	the prosthetic leg compared to when leading with the sound leg. The
	data showed that whether the TF subjects initiated a gait with their
	prosthetic leg or with their sound leg, their horizontal end velocity
	was equal. The subjects compensated the loss of propulsive force
	under the prosthesis with the sound leg, both when the prosthetic
	leg was leading and when the sound leg was leading. In the vertical
	CoM velocity, a tendency for differences between the two conditions
	was found. When initiating gait with the sound leg, the downward
	vertical CoM velocity at the end of the gait initiation was higher
	compared to when leading with the prosthetic leg. Our subjects used
	a gait initiation strategy that depended mainly on the active ankle
	function of the sound leg; therefore, they changed the relative durations
	of the gait initiation anticipatory postural adjustment phase and
	the step execution phase. Both legs were controlled in one single
	system of gait propulsion. The shape of the CoP trajectories, the
	applied forces, and the CoM velocity curves are described in this
	paper.},
  doi = {10.1115/1.2838028},
  institution = {Center for Human Movement Sciences, University of Groningen, Groningen,
	The Netherlands.},
  keywords = {Adult; Amputees, rehabilitation; Artificial Limbs; Computer Simulation;
	Feedback, physiology; Female; Femur; Gait; Humans; Leg, physiopathology;
	Locomotion; Male; Models, Biological; Physical Exertion; Pressure;
	Stress, Mechanical},
  language = {eng},
  medline-pst = {ppublish},
  owner = {hvk},
  pmid = {18298178},
  timestamp = {2011.12.20},
  url = {http://dx.doi.org/10.1115/1.2838028}
}
 
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