Joseph JA, Griffin MJ. Motion sickness: effect of changes in magnitude of combined lateral and roll oscillation. Aviat Space Environ Med 2008; 79:1019–27.Background: In tilting trains, low-frequency lateral and roll oscillation combine and can cause motion sickness. During a journey, passengers are exposed to motions of varying magnitudes, but the effect of a change in magnitude on motion sickness is not known. It was hypothesized that the rate of increase in motion sickness would be greater during exposure to a high-magnitude motion than during exposure to a low-magnitude motion and that there would be no difference in sickness between motions when the ‘motion sickness dose value’ was the same. Method: At intervals of at least 1 wk, 20 subjects were exposed to 4 conditions consisting of 0.1-Hz sinusoidal lateral oscillation with 50% roll compensation. Each condition had four successive 15-min periods of motion presented without a break (total duration 1 h). Each 15-min motion was either a high-magnitude motion (H) (±1.26 ms⁻² lateral oscillation with ±3.66° roll oscillation) or a low-magnitude motion (L) (±0.63 ms⁻² lateral oscillation with ±1.83° roll oscillation). The four conditions involved four different combinations of magnitude: 1) LLLL, 2) HHHH, 3) LHHL, and 4) HLHL. Subjects were seated in a rigid closed cabin and gave ratings of sickness at 1-min intervals. Results: Symptoms of motion sickness were experienced in 56 of the 80 sessions. The rate of increase in motion sickness was greater with the high-magnitude motion than with the low-magnitude motion. For the two variable conditions (i.e., LHHL and HLHL), there was no significant difference in accumulated illness ratings when the motion sickness dose values were the same (i.e., between 30 and 60 min of motion). Illness ratings decreased during periods of low-magnitude motion experienced after periods of high-magnitude motion and also after the cessation of all motion. Conclusions: With combined lateral and roll oscillation, the rate of increase in motion sickness is greater during periods of high-magnitude motion than during periods of low-magnitude motion. With motions having the same motion sickness dose value but different sequences of exposure, there were no significant differences in accumulated illness ratings at times when the motion sickness dose values were the same.