Connecting NURBS muscles into a Maya Muscle system lets you specify what points can actually be weighted to the muscle when doing Sticky weighting. If you paint weights to a point that was originally outside of the Sticky-bind distance, that point calculates its binding on the fly, slowing down deformation. In case you made your original distance too small, you can always go back and reset the Sticky bind information for a muscle to use a larger distance, or all points.
To re-bind the Sticky information for a NURBS muscle
The Sticky Bind progress window appears and the muscle can now use points based on the options you chose.