PBWS Modeling Project


The purpose of this project is to develop a complete biomechanical model of a patient undergoing partial body weight supported (PBWS) gait training. The model is developed using LifeModeler. Currently the PBWS system is modeled as a vertical force applied to the trunk. The applied force is an idealized approximation of the support provided by PBWS systems. In the next phase of model development, the mechanical components of the PBWS system will also be modeled. The control system for the PBWS system is developed using MATLAB/Simulink. Co simulations using the biomechanical model in the MATLAB/Simulink control loop will be used to expedite development of the next generation PBWS control system.


The following movies depict simulations based on the data of a person with left side hemiparesis. A view of the model kinematics is on the right. A graph of the ground reaction forces and, if applicable, the support force is on the left.

Data Driven Motion

Data obtained with the subject walking on the treadmill with no support. Position constraints dictate the kinematics. Hence the person is walking in place. Because of the position constraints, the ground contact forces are invalid.

Unsupported Simulation

Unconstrained simulation with muscles driving the limbs through the trajectories learned in the data driven simulation above. Because there are no position constraints, the person walk over ground and the contactg forces are realistic.

Constant Force

40% body weight support force (vertical acting on thorax) added to the simulation above. Solid lines indicate the ground contact force with constant support. The dotted lines are the contact forces when unsupported.

Counter Weight

Here the support force simulates a counter weight equal to 40% of body weight. Similar to constant support. Variance in the support force (red dashed line) is the result of acceleration of the weight due to body center of mass height changes. Zero friction assumed.


The support force is set to provide 20% body weight support. Because of the spring action of the support (k=800n/m), the support force increases significantly when the center of mass drops below the reference point .


Here the support force is 20% of body weight during weight acceptance and 10% of body weight during push-off.

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Last Modified: 01/03/05