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Stress Create is useful to move part of your rigging: first the joints, but also you can move controls.Stress Create will create a locator control on your selection: you can adjust the base movement, setting 3 parameters of locator (frequency, amplitude, multiply).You can to use 3 different type of stress:
-Curl Stress: is useful for curl movements of articulations, as elbow or knee (but also fingers' parts). It is made for non-root joint only.
-Bend Stress: is useful for wave movements of bones, as spine lateral bending or arms and legs bending.It is possibile choose between root joints or non-root joints.
-Crawl Stress: is useful for large, circular movements of articulations, as circular movements of shoulders.
In general, you can use “Stress Create” to test your character rigging, or can use it to correct the skinning of your character in real time, without the needed to move single parts manually or create some animation.
You can see some simple tutorials at the links below: