Just made my third stab at the Frankenmuscle, trusting that in 16.5 things have settled down a bit, but I'm getting the same result I always have in 16.0. See the attached file.

Created some muscle geometry and two muscle pins, and put the whole thing together using the Franken Muscle shelf tool. No joy. Digging into the frankenmuscle1 asset I see many errors, starting with the Bone Capture Biharmonic node (/obj/frankenmuscle1/muscle/bonecapturebiharmonic6). Looking at the rig, I see that the capture regions (/obj/frankenmuscle1/internal_core/capture_indices) are not in the muscle pin positions, but clustered around the origin. Since the cregions are nowhere near the geometry, nothing gets captured.

I've seen similar behaviour with the Muscle asset as well, in non-sphere mode. Since fumbling the muscle pin transforms would be a catastrophic bug, I've been assuming it was something I was doing wrong. Any ideas?

Houdini 16.5.309, MacOS 10.12.6, 2013 Mac Pro. The geometry in the attached file is locked, but I can provide the .geo file if necessary.

You'll need to establish a valid Capture Pose for your geometry and MusclePins.
To see the problem, on the FrankenMuscle:
-go to the Capture/Deform Tab
-activate Edit Capture Pose (All Rig Sources)
This will put all your franken rigs and your geometry in their respective captured positions. If your Pins are not intersecting the geometry, nothing will get captured.
When you're in Edit Capture mode, everything will turn blue.
You can drag your pins into position while in this mode and that can begin to fix the problem. If you do this, you'll likely need to adjust the animated positions of your pins as well.

However, a simpler way is:
-while your pins are *not* in Edit Capture Mode, ie, when they're in their “animated positions”, (colored red)
-Select your pins,
-Press Capture>Set Capture Pose
This will take the current pin positions & orientations and store them as the capture pose.

-j

Ah, that's very illuminating. Set Capture Pose does wonders. Thank you, John.