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 :
Casey is best known for playing Sgt. Gavin Troy on Midsomer Murders, and Anthony Cox in Our Friends in the North. He also played firefighter Tony Barnes in the 2004 ITV firefighting series Steel River Blues. He was also guest starred in M.I. High.