Biomechanical Evaluation of a Biomimetic Stand-Assist Toilet Seat for Older Adults: A Synchronized AI-Kinematic and Kinetic Analysis

Many older residential toilet designs may pose substantial biomechanical demands for older adults with reduced lower-extremity strength, as standard seat heights often require increased joint range of motion (ROM) and compensatory upper-limb support during sit-to-stand (STS) transfer. This exploratory, repeated-measures biomechanical study evaluated the effects of a biomimetic Stand-assist Toilet Seat (BSTS) designed to facilitate STS movement through a forward-and-upward curvilinear lifting trajectory. Thirty community-dwelling older adults were stratified into high-, moderate-, and low-functioning groups according to normative 30 s Chair Stand Test performance. Participants completed repeated STS trials under conventional and BSTS-assisted seating conditions in randomized order. A synchronized multimodal assessment integrating MediaPipe Pose-based motion tracking for sagittal-plane kinematic analysis was used to quantify lower-limb kinematics and upper-limb kinetics. Mixed-design ANOVA revealed significant main effects of seating condition on hip and knee ROM (all p < 0.001, η2p > 0.70), indicating reduced lower-limb joint motion requirements under the BSTS condition. Significant reductions were also observed in peak arm-support force (F (1,27) = 14.57, p = 0.001, η2p = 0.35) and arm-support impulse (F (1,27) = 20.21, p < 0.001, η2p = 0.42), demonstrating decreased upper-limb loading during STS transfer. No significant interaction effects between seating condition and functional group were identified. These findings suggest that the BSTS modified STS movement patterns and reduced upper-limb loading demands in community-dwelling older adults. The combined kinematic and kinetic assessment approach may provide a practical method for biomechanical evaluation of assistive seating technologies in rehabilitation and aging-related applications.