IOWA CITY — If the running game is the power source for Iowa’s success, then the running backs are the fuel, the atoms, the coal or whatever energy element you want to use.Going into Saturday’s game at Purdue (1-7, 0-4 Big Ten), the Hawkeyes (5-4, 2-3) find themselves in a bit of an energy crisis.Junior Mark Weisman, who remains Iowa’s leading rusher with 747 yards, sprained an elbow and missed much of the second half in last week’s loss to Wisconsin.