###### Abstract  
The purpose of this study was to investigate whether the use of a bathing assist device, \"Bath Assist\" (BA), could reduce the physical burden on caregivers providing bathing assistance and also alleviate the difficulty of bathing activities for care recipients. BA is a robotic device that is attached to bathtub. The seat can be raised and lowered using the water pressure from the shower tap. The four caregivers and four care recipients were paired one-to-one to simulate bathing activity, and the physical burden on each caregiver during bathing assistance was evaluated with and without the use of BA by observation, questionnaire, and wireless surface electromyography. For caregivers, BA transformed the task of assisting care recipients into and out of the bathtub into a monitoring activity. Additionally, the muscle activity of the caregivers' lumbar region, trunk, and upper limbs, which are used to assist care recipients out of the bathtub, was significantly reduced when using BA. Questionnaires confirmed that the use of BA reduced the physical burden on caregivers. These results indicate that BA has the potential to reduce both the physical burden on caregivers during bathing assistance and the difficulties care recipients experience during bathing. b +
Footnote †: journal: Medical  
be detached and functions as a fully reclining electric wheelchair, decreased the physical burden on caregivers during transfer assistance and allowed a care recipient to move easily and meet with their family members frequently in a nursing facility [15; 16]. Moreover, we reported that the long-term use of wearable transfer robots, such as the \"Muscle Suit\" (INNOPHYS Co., Ltd., Tokyo, Japan) and \"HAL(r), Lumbar Type for Care Support\" (CYBERDYNE, Inc., Tsukuba, Japan), led to the effective performance of transfer care tasks in nursing facilities [17]. These studies suggest that transfer support robots have the potential to decrease physical burden on caregivers and improve quality of care. Bathing care assistance is also considered to be a physically demanding task for caregivers in relation to transfer assistance [18]. In Europe and the USA, the use of welfare equipment, such as ceiling lifts, has been implemented to support bathing activity [19; 20], which has contributed to the prevention of back pain in caregivers [21; 22]. However, the introduction of bathing lifts is still limited in Japan due to their financial implications and the training required for caregivers. In addition, there are technical problems that installation of these lifts into homes is limited due to their large size and the need for construction work in the bathroom [23]. Nevertheless, the act of bathing in the bathtub, as well as showering, is recognized to be important not only to keep the body clean but also as a daily relaxation, which is a popular and often habitual pastime, at least in Japan [24; 25]. However, negotiating entry into a bathtub with slippery surfaces and a high threshold can be a difficult and dangerous activity for care recipients. Therefore, we believe that utilizing robotic technology to support bathing activity for care recipients and also their assistance by caregivers is highly desirable for realizing safe and secure nursing care. In 2020, a bathing support device, \"Bath Assist\" (BA, the HI-LEX Corporation, Takanazuka, Japan), was developed to support the bathing activity of physically disabled or older adults (Figure 1) [26]. This is a robotic-based device that, with the simple operation of a switch, can be used to raise and lower the seat with the water pressure by connecting the shower tap to the BA controller. Since BA is a compact size (the main unit: 625 mm \(\times\) 688 mm \(\times\) 946 mm) and can be attached to a standard bathtub, it is expected that BA can be used not only in nursing facilities but also at home. For those who need some assistance for bathing activity, the use of BA can foster independent living with dignity.