The effects of motion direction, body axis, and posture on motion sickness induced by low frequency linear oscillation.

A recent experiment demonstrated that low frequency linear oscillation through the Z-axis of the body was more nauseogenic when applied in the vertical direction, with subjects seated upright, than in the horizontal direction, with subjects supine.The nauseogenicity of low frequency linear oscillatory motion is dependent on direction of motion with respect to the gravity vector, orientation of body axis with respect to motion, and body posture.The following conditions were compared: A) seated upright, with horizontal motion, X-axis; B) seated upright, with vertical motion, Z-axis; and C) supine, with vertical motion, X-axis. Sinusoidal motion at 0.35 Hz, 3.6 m.s-2 peak was used in all conditions. Two experiments were performed. In Experiment 1 subjects (n = 28) were exposed to conditions A and B. In Experiment 2 subjects (n = 12) were exposed to conditions A, B and C.Horizontal motion (condition A) was found to be twice as nauseogenic (p < 0.05 to p < 0.0001) as vertical motion (condition B), but there was no difference in nauseogenicity between upright and supine postures for vertical motion (condition B vs. C). Mean motion exposure times to achieve moderate nausea were: Experiment 1: A) 9.0 min.; B) 22.4 min.; Experiment 2: A) 15.3 min.; B) 27.1 min.; C) 22.5 min.These results, taken together with those of the previous experiment, suggest that upright vs. supine body posture and stimulation through X- vs. Z-axis, both enhance the nauseogenicity of low frequency linear oscillation, these effects are additive, but that motion direction with respect to the gravity vector (horizontal vs. vertical) is a less important factor.