If you are applying the Muscle deformer to an object that has skinClusters, you can turn on Relative Sticky mode using the window that appears as you apply the deformer. See Apply the Muscle deformer.
If you have applied the Muscle deformer and chose not to turn Relative Sticky mode on at that time, you can still turn Relative Sticky mode on by doing the following.
To turn on Relative Sticky mode
The Muscle deformer Relative sticky attribute switches to relative (on) and a new cMuscleRelative deformer is created and connected. If a skinCluster existed on your object, the deformer is automatically placed properly just before it in the history list. If there was no skinCluster, the deformer is placed in the front of the history.
If you want to change
the order of the history for the cMuscleRelative deformer, 
-click
and select All Inputs to do the typical
reordering operations.
Set selected Muscle Objects to Relative Sticky mode
When using Relative Sticky weighting, you can independently set each capsule, bone or muscle to be in Relative mode or not. This lets you set one dummy capsule that never moves to be “Not relative” so that you can normalize Sticky weights with it. By default, they are marked as Relative.
To turn Relative Sticky mode on for an individual Muscle Object
To turn Relative Sticky mode off for an individual Muscle Object
