pump iron

pump iron {infml}
(to lift heavy metal objects as a form of exercise; to do exercises by lifting heavy weights in order to make your muscles stronger, to increase your strength, or to improve your appearance ) — качать мышцы, качаться

Example 1: These days both men and women pump iron for fitness. (thefreedictionary.com)

Example 2: According to a recent University of Southern Maine study, half an hour of pumping iron burns as many calories as running at a 6-minute-per-mile pace for the same duration.

Example 3: At Harvard Medical School and Tufts University, researchers asked a bold question. What if 10 old folks, nearly a thousand years old in combined age (this isn't dog years), began to pump iron? Not Geritol -- but simple leg exercises performed three times a week over eight weeks. Would these 90-year-olds, all rest-home residents, not only build up their strength but really see improvement in their lives from this moderate muscle pumping (Journal of the American Medical Association, June 13, 1990)?