Built into muscles are three states: Rest, Squash and Stretch. You can set what drives the muscle into these states, as well as what the center line curve looks like for the muscle in each state.
It is a good idea to set up these pose states before sculpting your muscle. This way you can be certain the poses you are sculpting are for the actual state you are in.
To set the state of the muscle
For example, you can go to the default/rest pose and click the Rest button, then put the model into a squash state using the bones/joints and click the Squash button, then do the same for the Stretch state.
It is important to set all three states for the muscle using these buttons before tweaking the attach positions or model. Internally, the Muscle Creator stores the relative change from the start attach object to the end attach object for the muscle. (You can see that “group” nodes are created and parented to the Start Parent curve that exists for the muscle.) This data includes information on how the child bone is rotated and translated relative to the parent bone. This information is then used to drive the different states on the muscle.
In addition, if you re-sculpt or adjust the two Attach Locators on each end of the muscle to better position it, click Reset Width. This resets the new locator distance to be the new default start/end widths for the muscle. This way, if the autoWiden attribute is used, the cross sections scale properly.
Now that the pose state data is stored, you can set the center line positions of the Attach controls. That is, you can adjust/move each of the Attach controls to set how the muscle looks in each state. For example, for a knee, you can adjust the attach states for a muscle so that when the knee is bent, the muscle attaches stay outside the bones and the muscle appears to slide over the front of the knee.
