Bedrest
Head-down tilt (HDT) bedrest is a well-established terrestrial model for some of the physiological changes occurring during spaceflight. Studies performed before, during and after bedrest allow both fundamental research, e.g. on mechanisms of the observed changes, and the evaluation of new countermeasure concepts for long-duration space exploration missions.
ESA has been organising bedrest studies regularly since many years, validating a wide variety of countermeasures such as exercise, artificial gravity, and nutritional supplements.