A Pennsylvania state trooper and plant security guards stand outside the closed front gate to the Metropolitan Edison nuclear power plant on Three Mile Island near Harrisburg, Pa., in 1979.
Paul Vathis, File Photo/AP
Paul Rider runs on Mulholland Drive in Los Angeles, March 25, 2011. Researchers say a moderate running regimen is actually beneficial for the joints of people with healthy knees.
Dennis J. Provost for NPR