There are two types of Control rigs in MotionBuilder, one that uses only Inverse Kinematics, and one that uses a combination of Inverse and Forward Kinematics. These two rigs are available so that you can choose what type of control best suits your project. Some situations may require fine tuning that may not be possible using Inverse Kinematics alone. In this case, you can use the FK/IK combination rig. Both Control rigs use special markers that let you adjust the position and rotation of a character’s bones and joints.
When using a rig that combines IK and FK, you can adjust the amount of reach between the two rigs. Adjusting the reach lets you control how much the rig follows the IK effectors in terms of rotation and translation.