Astronauts with Shuttle exposure were defined as those selected for the Shuttle program, along with those who were selected prior to the program, but who flew on Shuttle missions. The overall injury rate included astronauts who have not flown on the shuttle. Mission period analyses encompassed only those who flew between the April 1981 STS-1 and January 1998 STS-89 missions. The mission period was defined as the 1 year preflight and 1 year postflight periods, or a total of 2 years surrounding a mission. The medical data were obtained from periodic clinic visits, annual examinations, preflight and postflight examinations and consultant reports between January 1978 to March 1999. Only events occurring during the astronauts' active duty were considered in these analyses.
The overall injury rate for the shuttle astronauts was markedly greater than the rate for the comparison participants. This should not be surprising, as astronauts tend to be more physically active and are therefore more likely to sustain exercise related injuries, despite the fact that they are in a state of improved conditioning. Also, as compared to the astronauts' records, some under-reporting of comparison participant injuries is expected, as the JSC clinic is not the primary care provider for most users. Medical screening and routine care for the comparisons is much less intensive as compared to the astronauts. In addition, medical care for comparisons received outside of the JSC clinic may not necessarily be included in the LSAH database.
The astronaut injury rate within the mission period was almost three times that of the overall astronaut injury rate, while outside the mission period their injury rate was about half the overall rate. The difference between the injury rates inside and outside the mission period was statistically significant (p=0.000). This trend fits the previous expectation of increased injury rates due to more physical activity in the preflight training period, as well as the deconditioning of bones and muscles in microgravity.
Shuttle astronauts sustained injuries at a much higher rate than those sustained by the comparison participants. A higher injury rate is to be expected because astronauts, as compared to the comparisons as well as the population as whole, tend to be physically more active, and many participate in regular vigorous exercise. There may also be more complete documentation of injuries in astronauts' medical records. However, in the time period surrounding a mission, the astronaut injury rate is significantly higher as compared to outside of the mission period. Training for a mission, or physical deconditioning following spaceflight may contribute to this higher rate.
There was no difference in the injury rate between the preflight and postflight periods. However, in examining specific musculoskeletal injuries (excluding open wounds and all injuries at other sites), more neck and ankle injuries were sustained in the preflight period and more back injuries were reported postflight. The increased number of postflight back injuries is noteworthy and may be attributable to several factors, including deconditioning, failure of the musculoskeletal system to return to its preflight baseline, not adopting precautionary measures when lifting, or a combination of factors. The relationship between back injuries and spaceflight is difficult to ascertain, as back injuries are such a common problem.
As the actual number of injuries within the mission period was relatively small, the question of whether preflight training or postflight deconditioning contributes more to injuries is yet to be definitively answered. Postflight preventive measures could include a heightened sense of awareness, additional physical therapy for back strengthening purposes, and standard injury precautions. These measures, and others, may be of benefit by decreasing the number of postflight injuries. As more data are gathered, the distinction between the preflight training and postflight deconditioning effects on injuries may be better understood.
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