The Reach Translation and Reach Rotation sliders in the HumanIK Controls solve differences between the FK and IK rigs on a character.
When you set keyframes on the Control rig, both the IK rig and FK rig are synchronized: the IK and FK rigs appear on top of each other in the scene. However, when you play your animation, the interpolation of the IK rig and the interpolation of the FK rig may not match, because each rig solves differently. Between keyframes, the IK rig and FK rig may not occupy the same space.
The HumanIK Controls sliders in the Character Controls let you adjust the amount of influence each system (IK or FK) has on a body part when the two systems are out of sync. This gives you complete control of what happens between keyframes.
To adjust the influence each system has, select an effector in the Figure representation, then adjust the percentage of translation and rotation reach between the IK and FK rigs using the Reach Translation and Reach Rotation sliders. The cells of the Figure representation update to give you visual feedback on Reach settings. (See IK cell status.)
Use the following guidelines when adjusting reach:
