A former Massachusetts prison guard has pleaded not guilty to charges that he ran long-distance races while collecting worker’s compensation for an on-the-job injury he said made it impossible to do strenuous activities. John Cloutier of Freetown was released on personal recognizance at his arraignment Tuesday on worker’s compensation fraud charges in Suffolk Superior Court. Prosecutors say Cloutier suffered a work-related injury in July 2008, and collected about $56,000 in worker’s compensation benefits between January 2009 and March.