Edward Twiss

@Liesbeth thanks! That seems to be working better for me too. I was trying to change the properties of the muscles instead of focusing on the constraints.

@PHENOMDESIGN in response to your requests:
1) I'm thinking of the types of tables you see online in the Houdini documentation for the different nodes but relating to artist recreation of real world muscle and tissue behaviour. Sort of like the jello, rubber, solid etc settings in the new MPM solver. A good example is the tables for real world based IOR or PBR settings for shaders that are online and readily accessible.
Something like a very cut down version of this data as it relates to value ranges for the settings for the muscle nodes in Houdini would be helpful https://academic.oup.com/view-large/333867009 [academic.oup.com]
I'm thinking more as an online reference to keep open when configuring different muscle settings so you know a combination that should work already to give a certain look. Presets to start from in the nodes already configured would be ideal then a table reference of ranges to stay within so your sims don't blow up.
2) I'm not sure if you've seen it but the Unreal ML deformation Houdini .hip demo file has a good example of splitting the different body parts up for use in the tissue workflow. Splitting the muscles then merging them back together seems to work better than having a lot of tabs in a node for a lot of grouped muscles to keep track of. If you group the muscles by body parts you can then add tabs to separate out the settings for specific muscles within that group.

Personally I'm a fan of staying in vanilla Houdini if possible but if you want some ideas on tools that would be useful please send me a direct message and we can discuss. I've already put together a script to populate the muscle flex links for all muscles and procedurally generated activation lines for every muscle that I'm using a lot if you want that.
Also have you looked at Procedural Anatomy? There's a ton of stuff in there to learn from: https://www.procedural-anatomy.com/ [www.procedural-anatomy.com]
PA_Chris is a good guy to talk to more about this type of thing.

Cheers,
Edward

@Liesbeth, thanks!
Having a reference table that is based on simulating real world muscle behaviour would be really handy. A lot of the time I'm trying to get similar behaviour for different parts of the anatomy on different models that should be within a range of values. Even going from biped to quadruped has a lot of overlaps in anatomy definition so being able to quickly setup upper and lower arms for example means you can spend time refining rather than running endless wedges playing whackamole to try to track down the right combination of settings.