OBJECTIVES:
Astronauts returning from a long stay in space will be observed to learn more about the adaptive processes in the somatosensory system and the lower limb skeletal muscle and acquire data that could contribute to astronaut rehabilitation after returning from space. To accomplish the above objective, astronauts who have stayed for a long time in space will be studied to measure the following items before and after their stay in orbit:
(1) Comparison of muscle activation patterns in lower limb antagonistic muscles
(2) Blood flow measurement in the lower limb skeletal muscle
(3) Body sway balance measurement.

In the present study, based on the hypothesis that the factors that make it difficult for astronauts to walk immediately after their return from orbit and before re-adaptation to the ground are the unevenness in the state of the lower limb antagonistic muscles, which adapted to the long-term space stay, and the somatosensory regulation in the vestibular system and cerebellum, investigators aim to study astronauts who have stayed in space for a long time, observing them to learn about the process, including (1) co-contraction of the lower limb antagonist muscles, (2) lower limb skeletal muscle blood flow, and (3) center of gravity regulated by the somatosensory system are re-adapted to land, and acquire basic data regarding the re-adaptation process immediately after return.

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