In 1980 Alberca et al. described a patient with a syndrome of increased muscle irritability, who presented ondulating muscle rolling movements and electrically silent cramps, myoedema and muscle reactions to mechanical stimulation similar to myotonic response, suggesting a disfunction at myofibrillar level.
For c-3po, it was a costume, Anthony Daniels played c-3po: For R2-D2, It was a costume and a remote controlled robot. CGI was also used in the prequel trilogy. So, they had Kenny Baker to play him : And from Portrayal section of wookieepedia article on R2-D2 :
Today perpetual baller, Dwayne The Rock Johnson, who will appear in the upcoming film reboot of the series, shared the news that model Kelly Rohrbach will play the part of Pamela Anderson's character from the original, CJ Parker. And, there's no more fitting way to reveal the casting choice than with some slow-mo shots.