(science fiction - well, for the moment, at least, they haven't yet got it working like this =)
A type of "muscle" fiber, often joined togheter to form long bundles.
Basically, myomer bundles behave like animal muscle cells: Run electrical current through them, and they contract. In BattleTech, myomer bundles are the most central thing that gives BattleMechs their advanced mobility.
In BT, the first successful experiment to produce very powerful myomer "muscles" was done by professor Gregory Atlas and Team Musclebound. In Operation Musclebound Experiment 45-B, December 21, 2350, a 2 meters long, 10 centimeters thick myomer bundle was able to generate a well-controlled (well, more or less =) pull of over one metric ton. Dr. Atlas could only comment, "I think it's time to get rip-snorting drunk".
See also MASC.