Adjust the envelopes:Physique associates the biped with the mesh by means of the mesh's vertices.
Each biped part is surrounded by an area called an envelope, and mesh vertices
that lie inside an envelope are effected by that biped part. The default size of
an envelope depends on the size of the biped part, which you set when you
pose the biped.Often, envelopes must be manually adjusted to make the biped work properly
with the mesh. If you notice irregular spikes poking out from the mesh, it's a
good indication that one or more vertices lie outside of an envelope's area of
influence. You can see this effect by rotating the arm.1 Right-click the Top viewport to activate it and use Region Zoom
to view Dr. X's left arm.2 Select DrX Biped L Forearm and rotate it up and down.
Some vertices don't move with the arm.680 | Chapter 5 Character-Animation Tutorials