## 4 Discussion
For example, where patients have an FIM score in the range of approximately one to four (full assistance-light assistance) for moving up and down in the bathtub, and three to five (moderate assistance-monitoring) for getting into the bathtub, a caregiver's physical burden will be effectively reduced with BA. It is also necessary to select appropriate patients for the safe use of BA. In this study, we judged that despite the small sample size, the ability to maintain a sitting position independently was required to use BA safely. However, other aspects should be assessed to ensure the safe use of BA; for example, there may be a risk of the patient losing balance backwards when assistance is required to lift a patient's legs when stepping over the edge of the bathtub. To date, different types of bathing assist equipment, such as ceiling-type, sling-type, and floor-type lifts, have been developed to reduce the physical burden on caregivers. In Japan, the use of such equipment has been highly recommended, but only approximately 20% of nursing facilities have installed them. Their size and the need for construction work in the bathroom are likely to be the main factors preventing their introduction into homes. Other examples of welfare equipment that can be used to assist with bathing activities include bath boards, transfer benches, grab bars and stand assists (see OSHA's Guidelines for Nursing Homes [31]). However, since these devices do not have a lifting function, we consider them insufficient as benchmarks for comparison with BA. Unlike other comparable devices, BA is small enough to be installed in a normal bathtub and does not require any construction work, which may make it easier to introduce BA into homes. When installed in the home, the benefits of BA observed in this study may be helpful to family members as well as caregivers. In addition, the \"robotic shower system\" which automates the showering process, has been developed as a bathing aid in recent years [32]. This system would also reduce physical burden, but its installation requires construction work. As another solution, wearing an exoskeleton robot can reportedly reduce the physical burden on caregivers when providing bathing support [33, 34]. Our recent study showed that in a nursing facility where HAL, a wearable transfer support robot, has been used on a daily basis for more than two years, it has been utilized effectively not only for transfer assistance but also for bathing assistance [17]. In any case, assistance in the bathtub is one of the most strenuous tasks for caregivers, involving lifting the patient and maintaining a forward leaning posture on a slippery floor [6, 7, 8]. In this sense, the future challenge is to reduce the physical load on caregivers by incorporating these robotic technologies from various aspects. Lastly, the present study has some limitations that merit consideration. First of all, this study was not conducted in a bathtub filled with water because of the need to perform EMG recordings. Therefore, with a bathtub containing water, there is a possibility that the physical burden on caregivers and risk of accidents may be even higher since the floor and bath surfaces are slippery, and it is difficult to provide assistance when the body of a care recipient is wet. Secondly, the number of patients in this study was limited, and further research is needed to determine the effect of the degree of required assistance on the physical burden on caregivers. Thirdly, the method used to measure MVC by surface EMG recording in this study needs further investigation. In particular, the values of MVC of the quadratus lumborum muscle exceeded 100% when the caregivers provided bathing assistance. This may be due to the fact that the method used to calculate MVC was under isometric contraction conditions. Isometric MVC has been recommended as a normalization reference value if comparisons are sought between different muscles and individuals [35].