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In this Autodesk Maya muscle rig tutorial Video, I am Showing How to apply Muscles in Maya Rigging and advantage of Maya Muscle Plugin in Rigging.

Capsules are the Muscle primitive objects that you can connect to the Maya
Muscle skin deformer. They are basic Maya transform groups with a special
shape node underneath that is used to convert polygon or NURBS objects to
Muscle Objects that connect with skin.
Capsules are like Maya joints except that they have a shape and volume, which
allows them to be used for Sliding effects. When Sticky weighted to skin, capsules
deform the skin as they are moved, rotated, or scaled. This is similar to Maya
skinClusters. Sliding weights cause capsules to push out the skin geometry based
on their shape. Capsules can be non-uniformly scaled to get dynamic shapes.
You can create capsules from scratch or convert existing joints to capsules.
Any NURBS surface in Maya can be converted to have a Muscle Object shape
node and therefore can be connected to the Muscle deformer. In addition,
there are two tools that let you create two different types of muscles:
■ Muscles on page 6
■ Simple muscles on page 8
The main difference between the two muscle types is that simple muscles use
regular NURBS models with a special spline and spline deformer used to bend
them, while the new muscle is a parametric-style NURBS shape that has
deformation/posing ability.
Muscles
The Muscle Creator window lets you build a new, more powerful muscle with
rigging, shaping/sculpting, and deformation ability. These muscles include
two end points for each attach location so that you can more easily create
‘flat’ muscles and more easily orient your muscles. In addition, the Muscle
Creator window lets you grow muscles out to a surface. It is recommended
that you use these muscles for new rigs.
Some advantages of using this new muscle type include:
■ Adjustable resolution
■ Ability to mirror muscles after setup

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