These next gen carbon nanotube muscles have "diamond-like" stiffness side to side, but are as flexible as rubber when moved perpendicularly. When voltage is applied to the structures, they contract with a pulling force 30 times the force per unit of human muscles.
They're also quicker. A human's muscle fibers can contract 10% per second, but these can contract 40,000 percent.
I had no idea synthetic muscles materials have come so far. A few years ago, when I was covering JPL's robotic arm wrestling challenge for Wired, the materials had a fraction of the potential of organic muscles. [Wired]