Paralyzed "Superman" star Christopher Reeve, 49, broke his leg on Aug. 17 "during ongoing and routine physical therapy," his publicist said in a statement to the Los Angeles Times on Friday. The bone was reset the following weekend at the University of California, Los Angeles, Medical Center. The actor, who was paralyzed in a 1995 horse-riding accident, "is expected to resume his full regime of exercise in six to eight weeks," said the publicist, who added: "The cause of the break is unknown but is most likely due to bone density issues. For spinal cord patients there is a constant need to maintain bone density through regular physical exercise and physical therapy." Reeve, an activist in spinal-cord research, is now said to be recuperating at his home in New York.