The goal of this investigation was to characterize in a control group of subjects the effects of long-duration head-down bed rest on the sensorimotor functional reflex responses and to compare the responses obtained in the control group with those of a treatment group receiving a vibratory countermeasure designed to protect bone mineral density (BMD).
Subjects participated in three pre-bed rest test sessions to determine individual baseline responses. Test sessions were conducted during bed rest on days 5, 20, 40, 60, and 90 to determine whether a decrease in FSR or MSR amplitude occured. Another test was conducted immediately following bed rest to determine whether an increase in response was observed. Two additional post-bed rest tests (on +3 and +6 days following bed rest) were conducted to track response recovery.
This experiment has concluded in ground-based studies sponsored by the National Aeronautics and Space Administration's Human Adaptation and Countermeasures Division. This experiment was conducted during Bed Rest Campaigns 1 and 3A, 3B, 3C, 3D, and Campaigns 5A, 5B, and 5C. More comprehensive results can be viewed in the archived publication.
The effect of a week or two of bed rest, estimated from the mixed model regression analysis, showed that the population median start and peak latencies were increased by about 4.2% and 3.7%, respectively. Both of these increases were more than could be attributed to chance variation. However, there was no significant further increase in either latency as stays in bed increased to 90 days of bed rest. The median peak magnitude did not noticeably increase at the start of bed rest (0–18 days), but was estimated to increase by about 47% during the middle bed rest period (19–60 days). Peak magnitude measurements were much more variable than the start and peak latencies, thus there were too few subjects and measurements available to evaluate the possibility of a substantial increase during early or late bed rest.