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 :
Christopher Plummer and Al Pacino in Danny Collins.. Photo Credit: TNS / Hopper Stone. Al Pacino playing an overripe rock star ruing his misspent youth (and middle age) might seem like an opportunity for enthusiastic hoo-hah-ing and a whole lotta ACTING in capital letters. But the saving grace of Danny Collins is that Pacino is playing a performer, one whose overly large self is perfectly plausible.