Myomer takes fusion plant level energy to lift multi-ton limbs, but a lightbulb's worth of power can chuck a half empty water heater through a door and a chubby Precentor (Lost Destiny Ch 11). That same scene also gives us a little more detail on medical myomer, "[t]he myomer [used] in surgery is manufactured differently and has to be layered in with real muscle tissue to be useful. In surgery the stuff is used more like rubber bands." I would imagine a power source is implanted at this time, with the battery lasting for years at a time similar to a contemporary pacemaker battery, and replaced just as easily. Easier, in the case of removable limbs I'd imagine.