I am trying to understand what does it mean by the +/- sign of Proximal Distal (PD) joint reaction forces that contain in the selected output section.
For a normal gait simulation that include few steps, ankle and knee PD joint reaction forces always vary between 0 and negative values, whereas hip PD joint reaction forces always between 0 and positive values.
Does this mean that ankle, knee, and hip, only experience unidirectional PD joint reaction forces during normal walking? Does the negative (-) sign indicate that joint is in tension?
I appreciate any direction to clarify the above doubts.
There has been a lot of discussion on the interpretation of joint reaction force on this forum in the past.
I would like to point you to a previous post.
I would also like to point you to the wiki page where you can read more about this.
I would suggest you try to trace how exactly the joint reaction force is defined in selected outputs, specifically, what is the sequence of the segments in the joints. You would find that sequence of segments is inverted for the hip joint compared to knee and ankle joints. It's not great that this is not consistent in the leg model. I think we should fix this.
I hope this helps!