Joint Moment Measure Knee very lower than expected

Hello everybody,

I'm working in a simulation of hamstring exercises, this exercises consist in recreate a knee flexion, with 2kg in foot while thigh is vertical. My objective is observe activation in hamstring and coactivation in quadriceps. But results in simulation are really lower than I expected and I don't understand why that is happening.

I have put a force of 2kg in the foot with the function AnyForce3D:

AnyForce3D ForceFoot=
F = {0.0, -9.81, 0}*2;
AnyRefFrame &Ref_Foot2 = Main.HumanModel.BodyModel.Right.Leg.Seg.Foot;
AnyDrawForce Drw_Force1 = {

To recreate the movement, firts I lock all the joints except right knee, with the function AnyKinEqSimpleDriver, and I have recreated knee flexion with the function AnyKinEqInterPolDriver:

AnyKinEqInterPolDriver KneeDriver =
CType = {Hard};
Type = Bspline ;
FileName = "Pos_knee.txt";
AnyKinMeasure& Ref_Knee = Main.HumanModel.BodyModel.Interface.Right.KneeFlexion;

And finally, I have added the reaccions between pelvin and ground using AnyReacForce:

AnyReacForce PelvisReactions =
AnyKinLinear lin =
AnyRefFrame& femur = ....BodyModel.Right.Leg.Seg.Thigh;
AnyRefFrame &ground = Main.Model.Environment.GlobalRef;
AnyKinRotational rot =
Type = RotAxesAngles;
AnyRefFrame& femur = Main.HumanModel.BodyModel.Trunk.SegmentsLumbar.PelvisSeg;
AnyRefFrame &ground = Main.Model.Environment.GlobalRef;

My problem is the joint moment in right knee, according the simulation the right knee have a moment between -0.55 and -0.50 Nm during exercises but when I have calculated this moment, my results are between -20 and 0 Nm and I don't know what is wrong.

I also attach the model at the post if someone could help me to find the problem.


Pau Zamora (41.9 KB)

Hi Pau,

I think i have spotted an error in your code.

The KneeDriver will carry the loads...since it has reactions enabled this is default, so effectively you have an "engine" on the knee and the muscles will do nothing to flex the knee they will only be active to compensate other DOF in the model.

To fix it add this line in the knee driver.


Best regards

Hi Søren,

I have tried it and the simulation just working correctly.

Thanks you for your quick answer.

Best regards

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