During spaceflight or staying in other astral body, the load on the musculoskeletal system and hydrostatic pressure difference is decreased due to decrease in gravity. Thus, the skeletal muscle, particularly that in the lower limbs, is atrophied, and bone minerals are lost via urinary excretion. In addition, the heart is atrophied, and the plasma volume is decreased, which may induce orthostatic intolerance. The vestibular-related control is also declined ? in particular, the otolith organs are more susceptible to exposure to microgravity than the semicircular canals. Advanced resistive exercise device（ARED）with administration of bisphosphonate is an effective countermeasure against bone and muscular deconditioning. However, atrophy of the heart has not been completely prevented. Further ingenuity is needed against cardiovascular and vestibular dysfunctions. For advanced human space exploration, extravehicular activity suit with higher mobility and inner pressure, which make pre-breathing unnecessary. Countermeasure for radiation should be also considered.
