The University of Tokyo is going at creating animatronic muscles in an entirely different, yet simple to implement way. They basically use a block and tackle arrangement to multiply the torque of a coreless motor instead of gears.
A robot, activated with this approach reminds me of nothing so much as an antique sailing ship.
I am not much impressed with their robot's walking, but other movements are quite natural.
It apparently achieves a much better kw/kg ratio than more conventional robots.