# Knee Joint Forces

Dear the author of AnyBody,

I have two questions here regarding the Anterior posterior knee joint forces, I tried to search this topic in the threads discussion and I could not find any topic about it.

So, I hope this is not a repeated question.

Can you explain to me why is that the anterior posterior knee joint forces in negative value? is there anything to do with the direction of the vector matrix?

In the knee/ankle joint forces, we have 3 forces as the output, how can we read this output, which one is in X, Y and Z direction (F(0) or F(1) or f(2))?

Thanks for sharing
Kind regards
Groningen, NL

I added something to the Wiki:

Let me know if that explains the reference frames in the joints.

Dear Amir,

Thanks for the link, that helps a lot, but my first question about the anterior posterior knee joint, why was that negative, was not answered yet. Can you tell me why is that negative?

Thanks

I’m not sure If I’m getting you correct. If you draw and look at the Reference Frame in the Knee joint, you will see the A-P direction. So a positive value will indicate forces in the knee joint pointing in the same direction (A) and a negative value will point in the opposite direction §.

Dear Amir,

What I meant was: when we finished running the inverse dynamic analysis and look at : InversedynamicStudy/Output/HumanModel/SelectedOutput/Right/Leg/JointReactionForce/knee-anteriorposteriorForce

in that force, we see that the Knee A-P force is floating between negative and positif level, can you tell me why is that happens in concerning the A-P force in the knee?? which direction did cause the negative value, the anterior or posterior?

Thanks for sharing
Kind regards