Abstract

NASA: In a previous paper we suggested the use of two mechanically coupled counterrotating bicycles to prevent microgravity deconditioning during long term Space missions, the "Twin Bikes System" (Antonutto et al., 1991). The two bicycles, ridden by the astronauts, move along the inner wall of a cylindrically shaped Space module, thus allowing the astronauts to maintain their physical fitness while inducing along their body axis a centrifugal acceleration vector simulating gravity. However, regardless of the means to generate it, artificial gravity may lead to vestibular disturbances induced by the Coriolis cross-coupled angular accelerations of the semicircular canals due to simultaneous rotation about more than one axis (Benson, 1988 a, b; Nicogossin, 1989 b). Indeed, when a subject begins to rotate at a constant angular velocity around a fixed axis, as for example on a Barany chair, the semicircular canal of the vestibular apparatus centered on this axis sends a signal which fades in about 20-30 s. Thus if the subject does not move the head and has no ocular references, after the transient phase he feels still. Violent motional illusions arise, however, every time he tilts the head in pitch or rolls it. In these cases, in fact, the immediate disengagement of the previous "axial" semicircular canal leads to an illusive rotation in a direction opposite to the prevailing one. At the same time the engagement ex novo of another canal sends a signal correctly related to the new rotational situation. It is generally believed that the cross-coupled stimulation of two canals and the resulting sensorial conflict are the major determinants of "acute motion sickness" (AMS) (Young, 1984; Benson, 1988b).