Set these bones as ‘ Bone’.

Then it comes with a solver:

Select a piece of muscle, set it as ‘Tissue’, then it become:

hit play

looks bit soft, then we can change some setting here. By adjusting some values, I can make the tissue more harder and won’t swing too much.

quick select tool:

Muscle fiber and Action line:

the red lines on the surface are the muscle fiber

if the fiber directions are uncorrect, we can paint the fiber to fix it

After that, we need a curve to drive the muscle contraction, so I click the Create the Line-of-action Curve to generate a curve. Then using Rivet to bone to connect the curve to the bone.

select muscle and the curve then click the Muscle line-of-action.