`
#...connect attrs
def connect_attributes():
outputs_array = cmds.listRelatives(outputs, c=True)
muscleSystem_control = 'muscleSystem_CTL'
for muscle_group in outputs_array:
attrMassDensity = '%s_massDensity'%muscle_group
attrInertialDamping = '%s_inertialDamping'%muscle_group
attrYoungsModulusExp = '%s_youngsModulusExp'%muscle_group
attrMuscleGrowth = '%s_muscleGrowth'%muscle_group
attrYoungsModulus = '%s_youngsModulus'%muscle_group
zFiber_Array = [get_zFibersFromTissue(mesh) for mesh in get_meshTransformsInHierarchy(muscle_group)]
zFiber_Array = list(chain.from_iterable(zFiber_Array))
for zFiber in zFiber_Array:
zTissue = '%s_zTissue'%'_'.join(zFiber.split('_')[:-1])
baseMaterial = '%s_baseMaterial'%'_'.join(zFiber.split('_')[:-1])
#...connect inertialDamping
cmds.connectAttr('%s.%s'%(muscleSystem_control, attrInertialDamping), '%s.%s'%(zTissue, 'inertialDamping'), f=1)
print cmds.connectAttr('%s.%s'%(muscleSystem_control, attrInertialDamping), '%s.%s'%(zTissue, 'inertialDamping'), f=1)
#...connect youngsModulus
cmds.connectAttr('%s.%s'%(muscleSystem_control, attrYoungsModulus), '%s.%s'%(baseMaterial, 'youngsModulus'), f=1)
#...connect youngsModulusExp
cmds.connectAttr('%s.%s'%(muscleSystem_control, attrYoungsModulusExp), '%s.%s'%(baseMaterial, 'youngsModulusExp'), f=1)
#...connect massDensity
cmds.connectAttr('%s.%s'%(muscleSystem_control, attrMassDensity), '%s.%s'%(baseMaterial, 'massDensity'), f=1)
#...connect if loa found
if get_zFiberLOA(zFiber) != None:
#...turn on muscle growth and loa for zFibers that have a loa
cmds.setAttr('%s.enableMuscleGrowth'%zFiber, 1)
cmds.setAttr('%s.useLoaForMuscleGrowth'%zFiber, 1)
#...connect muscleGrowth for zFibers that have a loa
cmds.connectAttr('%s.%s'%(muscleSystem_control, attrMuscleGrowth), '%s.%s'%(zFiber, 'muscleGrowthScale'))
connect_attributes()
`
so i'm not sure if it works like this, since i don't exactly know what your external functions do. but maybe this helps for understanding. i think something like this could work.
I've moved the zFiber variables into the for loop, so that it only takes the corresponding muscle_groups.