Test 1: The Integrated Treadmill Locomotion Test characterizes alterations in the integrated function of multiple sensorimotor subsystems. This test required subjects to walk on a motorized treadmill while researchers assessed changes in dynamic postural stability, head-trunk coordination, visual acuity and lower limb coordination strategies.

Subjects walked at 6.4 km/h on a motorized treadmill while performing a visual task consisting of identifying the position of the gap in the letter "C" that is presented centrally on a laptop computer positioned 4 meters in front at eye level. Each trial lasted approximately 30 seconds and was repeated four times. Subjects also walked at 6.4 km/h on the treadmill while performing the same visual task described above, but in this case, with the letter "C" presented centrally on a micro-display positioned 50 centimeters in front at eye level. Each of these trials lasted approximately 30 seconds and were repeated four times. While subjects were walking on the treadmill and performing the visual task, 3-dimensional full-body motion data were acquired using a video-based motion analysis system; gait cycle timing was measured using foot switches placed in the shoes and dynamic visual acuity was assessed by the visual task described above.

Test 2: The Functional Mobility Test provides a corresponding assessment of the functional and operational changes in locomotor function by testing a subject's ability to negotiate an obstacle course placed over a medium-density foam floor. Subjects walked at a preferred pace through an obstacle course set up on a base of 10 cm thick medium density foam. The foam provided an unstable surface that increases the challenge of the test. The 6.0 m x 4.0 m course consists of several pylons and obstacles made of foam. Subjects were instructed to walk through the course as fast as possible without touching any of the objects on the course. This task was repeated three times in the clockwise direction and 3 times in the counterclockwise direction. The dependent measures are time to complete the course and the number of obstacles touched or knocked down.

RESULTS:

Test 1: Integrated Treadmill Locomotion Test
Results showed that subjects exhibited postflight changes in head-trunk coordination, toe clearance and gait cycle timing during treadmill locomotion. Dynamic visual acuity was decreased postflight, followed by an improvement in performance during the postflight recovery period. An analysis of the relationship between inflight treadmill usage characteristics and postflight functional mobility performance revealed that subjects who exercised on the iRED with greater body loading had enhanced postflight (R+1) functional mobility performance.

Test 2: Functional Mobility Test
Results indicate that adaptation to space flight led to a 62% increase in time to traverse the obstacle course on one day after return, and recovery of function took an average of 11 days after return.

In conclusion, recovery of functional mobility after long-duration space flight is composed of two distinct but interrelated motor learning processes: 1) rapid on-line strategic change characterized by immediate onset after landing and 2) slower adaptive change requiring days to complete after landing.

Postflight (R+1) changes in gaze control produced decreases in dynamic visual acuity (DVA) during walking. For some subjects, the decrement was greater than the mean acuity decrement seen in a population of vestibularly-impaired patients (collected using a similar protocol). The population mean showed a consistent improvement in DVA performance during the two-week postflight recovery period. Post-flight neurological exams conducted by flight surgeons have rated gaze and ocular symptoms from mild to severe in over 50% of returning Shuttle astronauts. These observations are consistent with the decrements in visual acuity during locomotion described in this report. Future work should focus on the addition of a “field” test of dynamic visual acuity that could be incorporated in the postflight examinations. This research should focus on the development of a portable system that will provide passive body motion (i.e. seated subject on a motion base) while subjects perform tests of visual performance. Astronauts should be tested as soon as possible after landing to assess the early effects of gaze dysfunction related to sensorimotor adaptation. This will allow a better determination of the potential impacts of changes in visual acuity on landing performance.

This research led to conduct of ground-based studies focusing on developing adaptability training programs that include both gait and manual control training. In addition this research is investigating the retention capabilities of adaptability training, allowing this type of training to be conducted preflight and therefore reduce the requirement for an inflight training component, thus saving inflight crewtime and upmass hardware requirements. It will be useful to examine the relationship between other in-flight exercise modalities (cycle ergometer, upper body resistive exercise) and post-flight functional mobility performance to determine if a relationship exists. The current in-flight exercise data set includes only average data from US crewmembers over the entire duration of the mission. The exercise prescriptions to US crewmembers are graded over the duration of mission with the intensity (especially loading) and duration increased towards the end of the mission. Hence, the above analysis may be overly conservative in its estimates and should be extended with data over separate in-flight periods to confirm the relationships observed in the present study.

Results obtained from this research helped motivate the design of the Functional Task Test, a pre/postflight battery of tests used to assess performance of astronauts on functional tasks that are representative of critical mission tasks for lunar and Mars operations. The Functional Task Test will allow better definition of the linkage between physiological change and functional performance including across several physiological systems (sensorimotor, cardiovascular, muscle performance).