Change and recovery of bone mass and acoustic properties of rhesus monkeys after Bion 11 spaceflight.

Bone mineral density (BMD) of lumbar spine and tibia, as well as ultrasound propagation speed along the tibia, was measured in Bion 11 flight and control monkeys. The flight monkeys showed a delay in the growth-related (L-1) bone mass increase compared to the preflight period. Similar changes were detected in some control animals. The changes occurred primarily in metabolically active spongy bone, as shown by ultrasound data.