The expected result for sensorimotor function is likely to be altered transiently by extended bed rest. While neuro-vestibular function is not likely to be affected, descending spinal reflexes and proprioceptive function may be altered. The neurological functions of all subjects will therefore be tested to establish a normative control population for the future. Otolith-spinal reflex function, integrated balance control performance, and functional mobility assessments will be made before and after bed rest to quantify the neuro-adaptive responses to this deconditioning stimulus. Importantly, by comparing flight data with bed rest data can determine the role non-vestibular factors play in postflight locomotor dysfunction.
This experiment was conducted during ground-based study sponsored by NASA's Human Adaptation and Countermeasures Division. More comprehensive results can be viewed in the archived publication.
FMT data were collected twice prior to bed rest, and on BR +0. Data were also collected on approximately day BR + 61 during the 90-d studies, and on days BR42, BR44, or BR49 for the evacuated subjects.
The FMT was developed to quantify an individual’s functional performance. In a recent comparison of common balance tests, the FMT, as used in this bed rest analog, correctly classified 88% of clinical patients with vestibular and balance disorders, outperforming the success rates of the more standard testing counterparts of Dynamic Gait Index, Time Up and Go, and the Berg Balance Scale. FMT data, used in conjunction with complementary test data, may highlight cases in which a subject’s central nervous system has reorganized its subcomponents to compensate for sensorimotor deficits. Moreover, FMT data is most informative when combined with other metrics of recovery of the sensorimotor system. Although all subjects received body massages in the current study, there appeared to be a marked difference in the subjects who did and did not receive a daily foot massage to ameliorate the tenderness of the soles of the feet as a planned countermeasure. It is unfortunate, given the current experimental design that we cannot separate the importance of the foot soreness on our results versus underlying changes in proprioceptive function.
The subjects who had sore feet (subjects who did not receive foot massage) performed much worse after bed rest (94% increases in time) compared to those who did not have sore feet (subjects who did receive foot massage, 27% increase in time). In comparison, data from subjects who have been in space for 180 d have shown a 50% change in their time to complete the course (TCC) on the same task. The difference between the spaceflight and bed rest results reflects the fact that bed rest mimics only sensory changes associated with axial body unloading without the concomitant adaptive changes in the vestibular system that is typical from spaceflight.