Blender Biceps Squeeze: Using a simple Bone constraint and a Helper Bone
To make Biceps squeeze with a forearm's motion, JorgeBenier5D put out a video where he used a Driver to adjust a helper bone -- the helper bone shifts along an axis, taking its linear motion from the rotation of the forearm.
See his video here: • Video
** I wanted to see if the Driver method could be avoided. **
So, this example, I just quickly made, uses only a Transformation bone constraint, with influence turned down (and the ranges set).
(Like Jorge, I dislike weight-painting, so the bones are positioned so automatic weighting of the mesh to the armature do the job.)
This was a quick test -- it was not intended as anything more than that.