Motion Builder Without Live Characters?

[lafortuj]

We are using two PPT cameras. Occlusion of the markers (making them inactive?) is the cause of the bizarre leg-lifts. I'm more concerned about the legs rarely bending. In the video, I had markers on both of my feet, my right calf, and my head. Even with the calf tracker, both of my legs seem unnaturally straight. Should I be using Inverse Kinematics better, or not at all? If I can make better use of IK, I'm sure a tutorial could be helpful.