leg (n.)
late 13c., from a Scandinavian source akin to Old Norse leggr "leg, bone of the arm or leg," from Proto-Germanic *lagjaz, with no certain ulterior connections, perhaps from a PIE root meaning "to bend" [Buck]. Compare German Bein "leg," in Old High German "bone, leg." Replaced Old English shank. Of furniture supports from 1670s. The meaning "a part or stage of a journey or race" (1920) is from earlier sailing sense of "a run made on a single tack" (1867), which was usually qualified as long leg, short leg, etc. Slang phrase shake a leg "dance" is attested from 1881. To be on (one's) last legs "at the end of one's life" is from 1590s.
leg (v.)
"to use the legs; walk or run," c.1500 (from the beginning usually with it); from leg (n.).