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The psychophysiologic effect of zero gravity, as experienced by someone falling freely in a vacuum (for example, astronauts in a stable orbit). A temporary state of simulated weightlessness can be achieved during powered flight within the earth's atmosphere by traversing an inverted parabolic curve where gravitational pull and centrifugal force cancel each other out.
Etymology: AS, gewiht + ME, les
a state of absence of apparent weight, as in being beyond the effects of gravitational force in space travel. See also space medicine.
Physiologic effects Bone mineral loss, altered blood chemistries, weakened immune system, variable heart rate, arrhythmias, loss of skeletal and cardiac muscle mass and strength, increased urinary loss of nitrogen and phosphorus, motion sickness, and redistribution of fluids that are normally pooled in the lower torso and legs, resulting in a ‘fat face’
in horses induces osteoporosis if the period of weightlessness is long enough; in dogs the effects of weightlessness are confused with those of head-out immersion in water.