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Skeletal Response (AP011)
Principal Investigator
Research Area:
Bone and calcium physiology
Species Studied
Scientific Name: Homo sapiens Species: Human

Bone is a living organ that is continuously remodeling itself. When mechanical forces applied to the skeleton during normal activity in a 1-G environment are removed, bone mineral is lost because bone resorption is greater than bone formation. Bone resorption represents a danger not only because of the risk of fracture in demineralized bones, but also because the concomitant increased urinary calcium excretion might increase the risk for the formation of kidney stones.

The purpose of this experiment was to determine the effect of microgravity on the skeletal system during space flight. Studies conducted during the Gemini 4, 5, and 7, and Apollo 7 and 8 missions used x-ray densitometry to measure the amount of bone mineral present in the os calcis, radius, ulna, and phalanges. The studies revealed significant bone mineral losses in all areas measured. The degree of loss appeared excessive for such short periods in microgravity. Further evaluation of the data determined that bone mineral loses were lower than what was first measured. The overestimates were primarily due to problems inherent in the measurement techniques used. Scientists concluded that x-ray densitometry was unreliable for calculating bone mineral losses. It was not until a much more stable method of measuring bone mineral content, called photon absorptiometry, was developed that bone mineral studies continued during Apollo 14, 15, and 16.

Early reports of significant bone mineral losses in the 5- to 14-day Gemini and Apollo missions emphasized the need for correlating mineral losses observed in ground-based studies with those observed during microgravity. Ground-based studies designed to mimic the microgravity condition were used to estimate when changes were likely to occur during a mission. Bed rest served as an experimental model since the loss of bone mineral in bed rested and immobilized patients had been observed during periods of up to 36 weeks.

It was determined during these studies that the amount of initial mineral content in the os calcis could influence the rate of mineral loss. Bed rested subjects who exhibited a high mineral content at the beginning of bed rest showed the least mineral loss both in percentage and in quantity. Conversely, subjects who exhibited a low mineral content at the onset of bed rest showed a greater rate of mineral loss. The bed rest model was also used to determine what remedial measures might be used to both reduce bone mineral loss and predict bone mineral losses in the astronauts.

Thus, another goal of this study was to establish time courses for both the bed rest and flight situations so that better estimates could be obtained on the risk of prolonged space flight as translated from the ground-based bed rest studies.

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Rambaut PC, Dietlein LF, Vogel JM, Smith MC Jr. Comparative study of two direct methods of bone mineral measurement. Aerospace Medicine. 1972;(6):646-650.[]

Rambaut PC, Smith MC Jr, Mack PB, and Vogel JM. Skeletal response. In: Johnson RS, Dietlein LF, Berry CA, eds. Biomedical Results of Apollo. Washington, DC: NASA Headquarters; 1975:303-322. NASA SP-368. [NTRS]

Vogel JM, Rambaut PC, Smith MC. Bone mineral measurement from Apollo experiment M-078. Houston TX: National Aeronautics and Space Administration; 1974. NASA TM-X-58110. [NTRS]

Vogel JM. Bone mineral changes in the Apollo astronauts. In: Mazess RB, ed. HEW International Conference on Bone Mineral Measurement, Chicago, Illinois, 12-13 October 1973.

Absorptiometry, photon
Bed rest
Bone and bones
Bone demineralization, pathologic
Bone density
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Data Information
Data Availability
Archive is complete. Data sets are not publicly available but can be requested.
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Bone mineral content : os calcis
Bone mineral content : radius
Bone mineral content : ulna

Mission/Study Information
Mission Launch/Start Date Landing/End Date Duration
Apollo 14 01/31/1971 02/09/1971 9 days
Apollo 15 07/26/1971 08/07/1971 12 days
Apollo 16 04/16/1972 04/27/1972 11 days

Additional Information
Managing NASA Center
Johnson Space Center (JSC)
Responsible NASA Representative
Johnson Space Center LSDA Office
Project Manager: Eric Gallagher
Institutional Support
National Aeronautics and Space Administration (NASA)
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