Exercise in artificial gravity

Abstract

Artificial gravity provided by short radius centrifugation is considered a promising countermeasure to the deleterious physiological effects of microgravity during long-duration space flight. We investigated the feasibility of dual countermeasures to address space flight deconditioning of the musculoskeletal and cardiovascular systems, by combining centrifugation with lower-body exercise. The exercise device is a small stair-stepper with constant resistance provided by dampers beneath each foot, and is the first such device to be used in centrifuge studies. We modified the existing centrifuge to support the additional stresses due to exercise and added following structural elements: support struts on the rotation shaft, a redesigned footplate to which the exercise device was mounted, and horizontal support beams. We also added a sliding mattress with linear ball bearings on rails, so that the subject's body can move up and down while stepping. Design changes and exercise feasibility were validated by having subjects exercise during centrifugation at 23 rpm. We measured heart rate, blood pressure, forces on the feet, and knee deflection due to Coriolis accelerations, for up to four subjects. As expected, heart rate and blood pressure did increase normally with exercise on the centrifuge, relative to when not exercising. However, both heart rate and systolic blood pressure were higher for exercise on the non-spinning centrifuge than on the spinning centrifuge, attributable to the necessity of pulling against the stair-stepper's dampers in order to exercise while lying supine. Approximately half the subject's weight was exerted on the footplate when not exercising.

(cont.) This was expected: since the subject's head was at zero radius and thus at 0-g radially, the 100% artificial gravity gradient along the body's longitudinal axis gave an average effective gravity of about 0.5 g. More pressure (up to 80% body weight) was exerted when the subject was stair-stepping. The measured lateral deflection of the knee during normal stair-stepping and knee bend exercises increased up to three inches compared to deflections in a non-rotating environment. This issue must be further addressed to determine if stair-stepping or knee bend exercises are to be used safely in artificial gravity.