Effect of toilet seat height and inclination on sit-to-stand motion for subjects with limited trunk mobility

This study aims to clarify the toilet seat height and inclination conditions that promote sit-to-stand motion for users with simulated kyphosis and reduced trunk mobility. The study was performed on healthy subjects with spinal orthosis to simulate a kyphotic posture and reduced trunk mobility (simulated kyphosis) in which the toilet seat was either not adjusted ("standard setting"), supplemented by 3 cm or 5 cm ("3 cm higher" or "5 cm higher"), or tilted forward by 5° or 15° ("5° tilt" or "15° tilt"). Subjective evaluation using sensory evaluation and objective evaluation using floor reaction force meter, three-dimensional motion capture, and electromyography were used for comparison. As a result, "5° tilt" and "15° tilt" were rated higher than the "standard setting" in the sensory evaluation of the sit-to-stand performance. This is attributed to the plantar load in the seated posture being higher in the two settings with the toilet seat tilted forward than that in the other settings. By contrast, the plantar load in the seated posture was lower in the setting with a raised toilet seat than that in the other settings. The plantar load in the seated posture was positively correlated with the height of the subjects. This study determines that under conditions of simulated kyphosis and reduced trunk mobility, tilting the seat forward increases the plantar load in a seated posture than "standard setting" and "higher settings", improving sit-to-stand performance of the user.