Three papers in this issue demonstrate new fiber-based designs within the world of artificial muscles, showing how these twisted and coiled designs can be controlled via heat, electricity and chemistry. The resulting artificial muscle material could find uses in miniaturized medical devices, microrobots, and "smart" textiles that respond to environmental changes, among other applications. Mehmet Kanik and colleagues developed a two-faced polymer fiber that can be created through a scalable iterative drawing technique, producing artificial muscles that are activated by heat and that can lift more than 650 times their own weight and withstand strains of more than 1,000%, while remaining resilient over thousands of use cycles. Jiuke Mu and colleagues describe a fiber type where power is provided by an electrothermally sensitive sheath surrounding tightly coiled inexpensive materials including commercial nylon and bamboo yarns. The contractile power of muscles built from these fibers is 40 times that of human muscle and nine times that of the highest power alternative electrochemical muscle. Jinkai Yuan and colleagues' contribution is a high-energy microengine composed of shape memory nanocomposite fibers that are twisted to store energy that can be released on demand after a small temperature change. In a related Perspective, Sameh Tawfick and Yichao Tang discuss how these innovations bring us closer to realizing pervasive automation across a variety of fields.