Human Test Subject Facility personnel maintain detailed tracking of each test subject's participation in all studies, their blood volume contributions, and any radiation exposure. To remain current in the test subject pool, physicals are repeated on a yearly basis. Subjects interested in participating in studies where blood or blood products are collected also have HIV and Hepatitis screens every 6 months.

Investigations using both male and female test subjects require approval by the JSC Committee for the Protection of Human Subjects. Major studies are presently focused on the effects of prolonged head-down bedrest (see www.bedreststudy.com for further details) and on the use of artificial gravity (human centrifugation) as a potential countermeasure to the adverse effects of prolonged bedrest. Other studies employ exercise protocols using treadmills, resistance devices, and cycle ergometers. Still others examine mechanisms of postural and/or gait instability, motion sickness, cardiac arrhythmogenesis (using advanced electrocardiography), orthostatic intolerance, immune deficits and deficits in dynamic visual acuity.

Evaluating selected countermeasures to space adaptation, testing medical devices and equipment, and training for microgravity exposure all benefit from the ability to simulate microgravity without leaving Earth's atmosphere are activities conducted as part of the NASA Reduced Gravity Program. NASA, having recently retired it's KC-135, now uses a C-9 similar to the commercial passenger DC-9 aircraft [KC/C9-135 photos] to fly parabolic arcs producing episodes of weightlessness lasting 20-25 seconds. A typical flight lasts 2 to 3 hours and consists of 30 to 40 parabolas. The C-9 also can provide short periods of lunar (1/6) and Martian (1/3) gravity. Over the last 35 years, approximately 100,000 parabolas have been flown in support of the Mercury, Gemini, Apollo, Skylab, Space Shuttle, and International Space Station programs.

Test Subject Facility personnel coordinate schedules for the C-9 and perform flight physicals for the investigators conducting experiments aboard the aircraft. The HTSF also provides support to university and other student groups whose experiments have been selected to fly aboard the C-9. With the increased frequency of Space Shuttle missions and the habitation of the International Space Station, the Reduced Gravity Program provides a truly ideal environment to test and evaluate space hardware and experimental procedures before launch.