1533, from L.
musculus "a muscle," lit. "little mouse," dim. of
mus "mouse" (see
mouse). So called because the shape and movement of some muscles (notably biceps) were thought to resemble mice. The analogy was made in Gk., too, where
mys is both "mouse" and "muscle," and its comb. form gives the medical prefix
my-/myo-. Cf. also O.C.S.
mysi "mouse,"
mysica "arm;" Ger.
Maus "mouse, muscle," Arabic
'adalah "muscle,"
'adal "field mouse." Fig. sense of "force, violence, threat of violence" is 1930, Amer.Eng. The verb first recorded 1913, "to accomplish by strength;" to
muscle in is 1929 in underworld slang.
Muscle-man was originally (1929) "an underworld enforcer;" sense of "strong man" first attested 1952.
Muscle-bound is first recorded 1879.
Muscle car "hot rod" is from 1969.
Muscular Christianity (1857) is originally in ref. to philosophy of Anglican clergyman and novelist Charles Kingsley (1819-75).