Consideration of tilting speed of lower back fatigue reduction system based on actively tilting seat

Users of visual display terminals (VDTs) are known to experience lower back fatigue because they remain in the same position while sitting for a long time. Our group developed an actively tilting seat to reduce the fatigue caused by maintaining one sitting posture. The possibility exists that high-speed tilting movement might have adverse effects such as disturbing the VDT work or inducing motion sickness. On the other hand, low-speed tilting movement might not sufficiently reduce lower back fatigue. However, the effects on long-time continuous VDT work have not been investigated. Additionally, even though various indices have been used to evaluate movements, the relationship among these indices remains unclear. Therefore, the purpose of this research is to investigate the effects of various tilting speeds on long-time continuous VDT work (a one-hour typing task) and the relationship between subjective and objective evaluation indices. In this study, the pitching movement of the seat around its horizontal axis was chosen as ± 3 degrees. We experimented with three pitching speeds of which the tilting periods (cycle times) were 13 s (0.078 Hz, 0.47 deg / s), 26 s (0.039 Hz, 0.094 deg / s), and 64 s (0.016 Hz, 0.24 deg / s). Objective evaluations were carried out by measuring the rate at which the density of salivary amylase changes, heart rate variability, pressure change on the seat, and effectiveness of the typing task. The density of salivary amylase changes and heart rate variability were measured for mental stress evaluation. Additionally, a subjective evaluation using the visual analogue scale (VAS) was conducted for each movement.