Heat engines have long been used for transportation, but electric motors, which deliver clean mechanical actuation and come in a wide range of sizes, have enabled the spread of automated motion used, for example, in pumps, compressors, fans, and escalators. Nonetheless, natural muscles, their biological counterparts, are far more ubiquitous. Human bodies have more than 600 muscles that drive functions such as heartbeat, facial expressions, and locomotion. There are many opportunities for expanding the use of actuators that mimic muscles by directly using electric, thermal, or chemical energy to generate motion and enable more pervasive automation. In this issue, on pages 150, 155, and 145, Mu et al. (1), Yuan et al. (2), and Kanik et al. (3), respectively, describe new types of fiber-shaped artificial muscles that exploit advantages derived from the mechanics of twisted and coiled geometries.

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