Rigging: Digital Orthopedia - Blender Foundations: The Essential Guide to Learning Blender 2.6 - page 256

Figure 9.16 The Inverse Kinematics panel in the
Bone context.

Figure 9.15 The reverse foot rig, complete.

Now, when you move the heel control, both translation and
rotation, the leg bones exhibit the proper behavior, following
and twisting with the foot. Figure 9.15 shows the completed
reverse foot rig.

Let's go back and tackle the problem of the knee bending
along more than a single axis. At the bottom of the Bone
context in Pose mode is a panel called Inverse Kinematics .
Shown in Figure 9.16 , it lets you set rules for each bone's
rotations while under the influence of IK. The x, y, and z
controls are enabled by default, meaning that the bone is free
to rotate along all three axes. To disable rotation around any
of them, just uncheck it. But which axis is which when it
comes to bones? Here's how to tell.

The Transformation widget that we used for object manipu-
lation back in Chapter 3 is very useful for working with bone
rotations. Enable the Rotation widget in Pose mode with
the Ctrl-spacebar hotkey, or by clicking the button on the
3D view header. The widget is visible in Figure 9.17 , set to

Figure 9.17 The Rotation widget in Normal space
for bones.