Exercise under artificial gravity - experimental and computational approaches

Abstract

Humans experience strong physiological deconditioning during space missions, primarily due to the weightlessness conditions. Some of these adverse consequences include bone loss, muscle atrophy, sensory-motor deconditioning, and cardiovascular adaptation, which may lead to orthostatic intolerance when astronauts are back on Earth. In order to mitigate the negative effects of weightlessness, several countermeasures are currently in place, particularly very intensive exercise protocols. However, despite these countermeasures, astronaut physiological deconditioning persists, highlighting the need for new approaches to maintain the astronauts' physiological state within acceptable limits. Artificial gravity has long been suggested as a comprehensive countermeasure that is capable of challenging all the physiological systems at the same time, therefore maintaining overall health during extended weightlessness. Ground studies have shown that intermittent artificial gravity using a short-radius centrifuge combined with ergometer exercise is effective in preventing cardiovascular and musculoskeletal deconditioning. However, these studies have been done in very different conditions, and confounding factors between the studies (including centrifuge configuration, exposure time, gravity level, gravity gradient, and use/intensity of exercise) make it very difficult to draw clear conclusions about the stimuli needed to maintain physiological conditioning in space. The first objective of this research effort is to analyze the effects of different artificial gravity levels and ergometer exercise workload on musculoskeletal and cardiovascular functions, motion sickness and comfort. Human experiments are conducted using a new configuration of the MIT Compact Radius Centrifuge, which has been constrained to a radius of 1.4 meters, the upper radial limit to fit within an ISS module without extensive structural alterations. The second objective is to develop a computational model of the cardiovascular system to gain a better understanding of the effects of exercise under a high gravity gradient on the cardiovascular system. The gravity gradient generated when using a short-radius centrifuge has not previously been investigated in detail. The model is validated with the experimental measurements from the MIT CRC. Then, the model is used to explore the cardiovascular responses to new centrifuge configurations and from 0g adapted subjects.