A manual powered treadmill includes a frame; a front shaft assembly coupled to the frame; a rear shaft assembly coupled to the frame; an intermediate shaft coupled to the frame, the intermediate shaft is disposed intermediate the front shaft assembly and the rear shaft assembly; a running belt disposed about the front and rear shaft assemblies, the running belt defining at least a portion of a non-planar running surface; and a safety device coupled to the intermediate shaft. The safety device is operable to substantially prevent movement of the running belt in a first direction and to permit movement of the running belt in a second direction opposite the first direction.