THE EFFECTS OF MOTION DIRECTION, BODY AXIS, AND POSTURE ON MOTION SICKNESS INDUCED BY LOW-FREQUENCY LINEAR OSCILLATION

Background: 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. Hypothesis: The nau seogenicity of low frequency linear oscillatory motion is dependent on direction of motion with respect to the gravity vector, orientation o f body axis with respect to motion, and body posture. Methods: The fol lowing conditions were compared: A) seated upright, with horizontal mo tion, 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 perf ormed. 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. Results: Horizontal motion (condition A) was found to be twi ce as nauseogenic (p < 0.05 to p < 0.0001) as vertical motion (conditi on B), but there was no difference in nauseogenicity between upright a nd supine postures for vertical motion (condition B vs. C). Mean motio n 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. Conclusions: These results, taken together with those of the prev ious experiment, suggest that upright vs. supine body posture and stim ulation through X- vs. Z-axis, both enhance the nauseogenicity of low frequency linear oscillation, these effects are additive, but that mot ion direction with respect to the gravity vector (horizontal vs. verti cal) is a less important factor.