Hello Colleagues,

 

Can anyone tell me if the prosthesis for an Above Knee (AK) amputee runner requires knee torque to swing the foot/shank forward before foot strike?

 

I work with two models; the spring-mass model (1) and a two-segment mechanical leg model (2).  I use the models to calculate the mechanical power expenditure of a human runner. 

 

The first model calculates the mechanical power due to CM motion and leg-spring compression.  The second model calculates the power required to accelerate the swing leg from its toe off position to its position at foot strike.

 

I am having trouble with the knee torque for the swing leg.  It seems as if it is quite small compared to the hip torque.

 

Does anyone know if knee torque is generally required in a prosthesis for an AK amputee runner?

 

Sincerely,

 

Ted Andresen
St. Petersburg, FL

 

If you are interested, you can find more information on the models below.

 

(1) The spring mass model is described at:

 

 

(2) The two-segment leg (2SL) is a double compound pendulum suspended from a hip joint that is follows the trajectory obtained from the spring-mass model. A sample diagram of a stationary double compound pendulum is shown at:

 

 

In this 2SL model the masses and radii of gyration for the segments are based on D. A. Winters Anthropometric Parameters as shown at:

 

 

The accelerations for the swing leg segments are then derived from a Lagrangian formulation. The accelerations are integrated numerically with a Runge-Kutta algorithm to give the path of the segments over the gait cycle.  A Newton-Raphson algorithm adjusts the hip and knee torques until the swing leg configuration at toe-off matches the configuration at foot strike.  Finally, the torques and swing angles are integrated to determine the work that is required to move the swing leg from one configuration to the next.