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 :
Top: The movie cast (from left to right): Vincent Piazza as Tommy DeVito, Erich Bergen as Bob Gaudio, John Lloyd Young as Frankie Valli, and Michael Lomenda as Nick Massi. Bottom: The real Four Seasons (from left to right): Tommy DeVito, Bob Gaudio, Frankie Valli and Nick Massi.