Hi Geordie !
Increasing Collision resolution will help to certain extend but sim time will increase. But if the muscles are very thin, i would suggest adding slide constraint will help or You could try making those thin muscle as sub Tissues .
Usually I follow these steps while doing Fat sim.
- Get the decent tet resolution especially arm pit , crotch area etc . Paint those area to hold the details.
- Set the optimum collision resolution and put on the self collision on fat tissue.
- If i don't get good collision than play around with the contact stiffness of tissue and and bones .
- Make sure to have enough sub set during sim.
- Lastly add the slide constraint.
On the side notes u could also try coupling muscles and Fat together.