An Ergonomic Evaluation of Physical and Mental Loads in Standing-up Motion from Forward-Sloping Toilet Seats

Abstract

We aim to develop a new in-home assistance system to aid in the standing-up motion from toilet seats in assisted bathrooms. The underlying design concept for accessible toilet facilities is to use a novel compact actuation device—a metal hydride actuator with several unique properties such as softness, noiselessness, and being lightweight—for tilting a toilet seat when required, thus helping elderly or frail people to stand-up after excretion. This ergonomic study evaluates the easiness of the standing-up motion using both objective and subjective data from healthy participants, as a prior step before developing the envisaged toilet seat tilting system. In the experiment, the participants were monitored to obtain simultaneous objective data concerning muscle activity, 3D body motion, center of pressure, and seat pressure distribution. Additionally, all participants were requested to provide subjective data (comfort scores) while standing up from a toilet seat under four different conditions—four different forward-tilting angles (0°, 5°, 10°, and 15°). All participants repeated the motion 25 times for each tilting angle, and provided feedback regarding their standing-up experience and feelings under each condition. According to the collected subjective data, a toilet seat tilt angle of approximately 10° increased the easiness and comfort of the standing-up motion. However, according to the measured objective data, the standing-up motion has individual variations in the electromyogram magnitude, center of pressure excursion, and seat pressure pattern, implying that to analyze the standing-up motion both the measured objective data and the perceived subjective data must be considered.