A stair-stepper for exercising on a short-radius centrifuge

One requirement for long-duration spaceflight is provisions for exercise to prevent deconditioning. We evaluated the feasibility of using a stair-stepper on a short-radius centrifuge for this purpose.

A stair-stepper was implemented on a centrifuge with a 2-m radius. There were 13 subjects who performed stepping exercise in a supine horizontal position while spinning at 0, 12.5, 23, and 30 rpm. They were instructed to step as fast and hard as possible during each 2-min session. We measured the forces on the feet, the heart rate, BP, stepping cadence, and medial-lateral deflections of the knees due to Coriolis forces.

Subjects completed the 2-min sessions successfully. Voluntary cadence of exercise and foot forces increased as rotation rate increased (average of 68 steps x min(-1) at 0 rpm and 91 steps x min(-1) at 30 rpm). Foot forces during exercise increased from an average of 43% bodyweight at 0 rpm to 84% bodyweight at 30 rpm. Heart rate and systolic BP increased with exercise compared with rest at each rotation rate, but the change was smaller as rotation rate increased (average of 134 bpm at 0 rpm and 128 bpm at 30 rpm). Medial-lateral deflections of the knee during exercise while spinning were significantly greater than when not spinning in some cases.

Presumably heart rate and BP were higher during exercise on a static centrifuge due to the muscular work required to pull with one foot while stepping with the other in a supine position. Subjects can sustain greater ground reaction forces when exercising than when lying still on the centrifuge (in some cases, greater than the full bodyweight). Medial-lateral knee deflections are a potential problem and should be monitored in future rotation studies.