A system and method that provide a prophylactic treatment to a person, e.g., a patient, to avoid the occurrence of pulmonary embolisms by the system providing neuromuscular stimulation to a person's lower extremities, e.g., the person's legs, when the system senses that a person has been immobile for an extended period of time. An implantable neuromuscular pacer, such as that described in U.S. Pat. Nos. 5,193,539; 5,193,540; 6,164,284; 6,185,452; 6,208,894; 6,315,721; 6,564,807; and their progeny, may be used to provide to selectively provide such stimulation. Preferably, such a device may be battery powered so that it can operate independent of an external apparatus. In particular, systems and devices of the present invention preferably additionally include an activity monitor, e.g., an accelerometer or the like, that disables or limits stimulation to pronged time periods in which there is limited activity.