In preparation for longer duration manned spaceflight onboard the Space Station Freedom, many new challenges face the aerospace medical community. It has been documented that cardiovascular, musculoskeletal, and neurosensory deconditioning result from prolonged exposure to a microgravity environment. These physiological alterations associated with spaceflight must be minimized to guarantee effective in-flight performance, functional return to a 1-g environment, and nominal rate of postflight recovery. In an effort to retard the deleterious effects of space adaptation, NASA has defined requirements for an Exercise Countermeasure Facility (ECF)within the Space Station Crew Health Care System (CHeCS). The application of exercise as a countermeasure to spaceflight-induced deconditioning has been utilized in the past by both the United States and the Soviet space programs. The ECF shall provide exercise hardware, physiological monitoring capabilities, and an interactive motivational display system. ECF operations and data shall be coupled through the Space Station Freedom Data Management System for monitoring of in-flight training and testing from ground control; thus, allowing for real-time evaluation of crewmember performance and modification of exercise prescriptions. Finally, the objective of the ECF is to monitor and control the exercise of crewmembers for the maintenance of an operational level of fitness to ensure mission success.