From Longman Dictionary of Contemporary Englishpump ironpump ironinformalDSO to do exercises by lifting heavy weights → pump
Examples from the Corpus
pump iron• And keeping in shape with her is a lot better than pumping iron.• Before I met her I used to pump iron.• They pump iron for hours every morning.• In any case, farmer's boys have no time to make hay before they are pumping iron not milk.• Yes, even his face was muscular, as though he pumped iron with his ears. 