In recent months, Cameron has sought to bulk up his shadow cabinet.
Also, he lifted weights with his teeth to bulk up his neck and trapezius muscles.
Chris Evans endured months of nausea-inducing workouts to bulk up for Captain America: The First Avenger.
mid-15c., "a heap," earlier "ship's cargo" (mid-14c.), from a Scandinavian source akin to Old Norse bulki "a heap; ship's cargo," thus "goods loaded loose" (perhaps literally "rolled-up load"), from Proto-Germanic *bul-, from PIE root *bhel- (2) "to blow, inflate, swell" (see bole).
Meaning extended by confusion with obsolete bouk "belly" (from Old English buc "body, belly," from Proto-Germanic *bukaz; see bucket), which led to sense of "size," first attested mid-15c.
"swell, become more massive," 1550s (usually with up), from bulk (n.). Related: Bulked; bulking.