Rigify leg issue

Question

I'm having an issue with a Rigify armature I made where the leg bones bend in the wrong direction at the knee bone. I checked the pole targets, and they seem to be in the right location. I posted the blend file so that you can see the issue for yourself.

Answer 1

As explained on Bone Positioning Guide — Blender Manual

You need to add "a slight bend to the knee" (and also elbows):

This is needed for the IK solver to know in which direction to bend the chain.

Be careful to have the bend in only one local axis of the bones, and keep the bones aligned. Otherwise, it will bend in multiple axes at once, and it will be quite a headache to control for the animator.

To straighten your leg

1. Enable X mirror so to automatically make changes on both sides of the rig:
   
2. Select the heads of your left hip and foot bones:
   
3. Snap your cursor to your selection by pressing ⇧ ShiftS > Cursor To selected. You should have the cursor about where the knee is:
   
4. Select the knee bone's head and snap it to the cursor via ⇧ ShiftS > Selection to Cursor:
   
5. Select the knee and hip bone, and recalculate their roll by pressing ⇧ ShiftN > Global +Y Axis:
   
6. Press , to set your Transform Orientation to Normal, so to more easily edit the knee's head position without creating unwanted bends:
   
7. Use only the Y axis to change the knee's height, and use the Z axis to introduce a slight bend for the IK solver to pick up the bend orientation:
   

For the arms: same procedure, instead use Global -Y axis at step 5.