Could someone please advise on how to achieve the fluid motion seen in Ziva muscles within Houdini? I've attached a video demonstrating Ziva muscles sliding smoothly while maintaining volume. However, in Houdini, the muscles don't slide smoothly, lose volume, and develop wrinkles. I've attempted to implement sliding constraints between muscles, but this only exacerbates the issue with more wrinkles and vibrations. How can I resolve this? Currently, I'm using sliding constraints between muscles and bones, but when applied to the tissue mesh, it lacks detail regardless of mesh tightness. In contrast, Ziva muscles display all details effortlessly without any adjustments to tissue settings. How can I replicate this fluid motion in Houdini's muscles?

It's hard to say with a video alone. As Houdini's muscle system is based on Vellum, you might need to tweak the solver settings to have enough iterations. Or there could be some other set up issue. I think it's best to post a hip file if you can.

Hello @edward, I've been experimenting with various iteration settings, but regrettably, I haven't been able to achieve the desired realistic result. I've attached the file for your review, and I would greatly appreciate it if you could take a look to help me identify any mistakes or oversights in my setup. Thank you for your assistance.

Here's my quick take on it.... As Edward points out, our system is based on XPBD, which is fundamentally different in the way simulations are handled. Over-constraining can lead to problems when the geometry's shape stiffness can't put up a decent fight with the constraints that push and pull on its points.
I took a stab a generating something closer to your mp4. I reduced the number of tets coming out of MuscleSolidify (fewer points = fewer constraints), and then tweaked the properties a little.

The other thing I added, since smoothness was an issue -especially with the thinner tendon areas- was to use a DeltaMush sop on the output surfaces.

If you can share an example setup that includes your tissue I'd be happy to look at that too.

Hi @John, I have prepared a file which is enclosed for your ready reference as suggested by you along with a few more questions, I hope you will help me to find the desired resolution to my questions/issues.

Here are the issues I have faced so far where I find Ziva has an edge over Houdini Muscle.
1. Why does the output of the tissue simulation differ when I incorporate data from smooth muscle? It appears to give decent results but gets too wrinkly on some occasions, don't know how to control it without damaging the appearance of muscle deformation and movement.
2. Between frames -17 to -12, the hand muscles are not properly attached to the bones. I attempted to address this by adjusting the velocity stiffness factor in the muscle bones tab and increasing the velocity blend for each muscle. However, these adjustments did not yield the desired outcome, prompting me to disable these values in the end. Can you guide in resolving this issue?
3. I'm wondering if there's a way to disable muscle collision with bones. In Ziva, this can be easily accomplished by turning off muscle collision for the palm muscles. However, I haven't found a similar option here.
4. How can I configure the sliding option to prevent excessive downward movement of muscles? In Ziva, applying a sliding constraint restricts muscle descent while enabling effective muscle compression. This is evident in the bicep muscles, which produce excellent results due to the sliding constraint please check the file provided.
5. Is there a method to disable all procedural constraints simultaneously? I find it cumbersome to use the default generated constraints as to me it appears to hinder more than support the simulation, I think the fewer constraints would make it easier to debug and faster to simulate muscles.
6. Is there any distance threshold option using a paint tool to adjust constraints?
7. In the muscle paint SOP, is there a way to revert to default paint values? Occasionally, I find myself needing to undo my painting work and return to the original settings.
8. Is it possible to assign different properties to distinct portions of a single muscle? For instance, can one half be designated as hard while the other remains soft? While I grasp the concepts of relative and absolute properties, this specific scenario eludes me.
9. How can I reduce muscle tightness around the elbow area?
10. What might be causing the lack of smooth mesh output in the tissue simulation, please check the file.
11. When I remesh to a lower count, the finger tendons shrink in size and no longer match their actual proportions, how do you manage such issues though the simulation in the attached file is done on the settings suggested by you?

https://drive.google.com/file/d/1e5Rc2ccgpyax0--ZhCDmhqK-dX3qni_R/view?usp=sharing [drive.google.com]