Definition of "bulk up" [bulk up]

• To gain weight. (verb)
• To train the body with a high-calorie diet and intense weightlifting in order to increase the overall mass of the body, especially the muscles. (verb)

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• "It has no real weight room, and one Olympic pairs champion, Artur Dmitriev, used to bulk up by moving the cases of beer into the Yubileiny café."
• "American cattle producers from Texas to Tennessee ship their herds each summer to the Flint Hills region of Kansas, where the animals bulk up on grass before they're dispatched to feedlots and then slaughtered."