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Current countermeasures to space flight related physiological deconditioning have not been sufficiently effective. We believe that a comprehensive countermeasure is the combination of intermittent centrifugation (artificial gravity) and exercise. We aim to test the long-term effectiveness of this combination in terms of fitness benefits. As a first-order determination of effectiveness, subjects participated in an eight-week exercise program. Three times per week, they exercised using a stair-stepper on a short-radius (2 m) centrifuge spinning at 30 RPM, maintaining a target heart rate that was systematically increased over the exercise period. During the sessions, foot forces and stepping cadence, heart rate, and perceived exertion were measured. Before and after the eight-week exercise program, measurements included: body fat percentage, bone mineral content, quadriceps extension strength, push-ups endurance, stepping cadence for a given heart rate, and maximum stepping endurance. We find that stair-stepping on a centrifuge is safe and comfortable. Preliminary fitness results indicate that stair-stepping on a centrifuge may be effective in improving aerobic fitness, body composition, and strength. These results indicate that such a combination may also be effective as a countermeasure to space flight deconditioning.

It is necessary to characterize the vestibular response associated with head movements for various centrifuge rotation rates if one is to explore short-radius centrifugation as a viable form of artificial gravity for future spaceflights. An existing motion sickness model was modified to design an adaptation protocol to facilitate head movements at a centrifuge speed of 30 rpm. Modification involved addition of a quantitative sensory conflict model to serve as the input to the motion sickness model. Sensory conflict in this context was based on the dynamics of head movements during centrifugation as well as a previously developed transfer function relating angular accelerations to semicircular canal firing rates. Additionally, an adaptation parameter based on comparison between model predictions and previous experimental results was added. A 3-day incremental adaptation protocol was conducted in which 16 subjects successfully made 30 yaw head movements during rotation at 30 rpm on day 3. Motion sickness results showed good agreement with model predictions and demonstrated the feasibility of adaptation to increasingly high rotation rates.

A fundamental lower limit to the radius of an artificial gravity centrifuge for long duration human space flights is the high rotation rate needed to achieve the acceleration needed at the rim. At high angular speeds, head movements out of the plane of rotation produce unexpected and disturbing Coriolis forces and cross-coupled angular accelerations, which lead to motion-sickness and disorientation. Previous studies in slowly rotating rooms set the practical upper speed limit at 6 rpm. Our research on intermittent repeated exposure to a short (2 m radius) high speed ( 23 rpm , 138 ∘ / s ) centrifuge has shown that most subjects can adapt to such head movements in a short time, and retain adaptation over days or weeks. The practical implications of this include the use of intermittent short radius centrifugation for long duration flights and the possibility of adapting astronauts to the unusual stimulus before flight. Theoretical issues include the possible development of a generalized internal model to describe the effects of Coriolis forces, as opposed to the development of families of stimulus–response relationships.