I am animating some extreme posing driven by a bvh engine now.
Some file went okay, but some have greases and artifacts.
In my rig in 3ds max, I've tested on very basic level
that the rotations of the limbs are acceptable.
But when the file is imported to the bvh engine,
this doesn't hold true anymore with some ugly looks.
For the skin weights, I give the joint areas
some blue regions for upper and lower arms so that they both
contribute the the weights, but I still got broken arms and legs,

arms piercing thru body
or something in the bvh animation....
Why?
Thanks
Jack

Reminds me of a problem I had when I tried making my own engine.

In my experience it was that the engine couldn't read multiple weights from different bones.

The general problem is that your engine isn't reading the bone weights the same as Max.The common work around is to model the mesh so that it deforms better with automatic weights.

I could try and explain it, but I am bad with words so check this instead: http://wiki.polycount.com/wiki/Limb_Topology

Also look at reel joints, you will notice that the joint and the fold don't sit directly behind each other.

it is exactly what ScoutingNinja said, or you need more edgeloops to create less burden on the "weights" system.