Here's from the Poser Forum FAQ, see the link above: Q: Why do the knees sometimes lock when I use the Walk Designer with my figure? A: This is known as "Gimbal Lock". It occurs when Poser has to bend two body parts (thigh&shin) that are aligned in a straight line. If two body parts are relatively straight. Poser doesn't know which direction to bend them and it takes a few milliseconds for it to figure it out. Producing a weird little glitch every time it tries to bend them. You can get rid of this by helping Poser decide how to bend the legs by selecting the HIP of the figure in the first frame of your animation. Then translate it down a little so the knees bend slightly.