must these relax only by dissipating heat, or can an applied force stretch them out again quicker? that would make it like real muscular systems, which must wo

must these relax only by dissipating heat, or can an applied force stretch them out again quicker? that would make it like real muscular systems, which must work in systems of opposition since actuation is one-way only (relaxation requires an opposing muscle, or some other force like gravity, to stretch it back out).