A significant number of non-institutionalized older adults have difficulty rising from a chair. Although there exist several assistive devices to aid with sit to stand, there is a lack of research that compares and analyzes various modes of assisted sit to stand to characterize their relative effectiveness in terms of biomechanical metrics. In addition, few existing assistive devices have been designed specifically to share between the user and the device the force required to rise, an approach that has the benefit of maintaining both the mobility and muscular strength of the user.

This thesis advances our understanding of different modes of load-sharing sit to stand through empirical quantification. A specially-designed sit-to-stand test bed with load sharing capabilities was fabricated for human-subjects experiments. In addition to an unassisted rise and a static assist using a grab bar, three mechatronic modes of assist, at the seat, waist and arms, were implemented. The test bed employs a closed-loop load-sharing control scheme to require a user to provide a portion of the effort needed for a successful rise motion.

Experiments were performed with 17 healthy older adults using the five aforementioned modes of rise. Force and kinematic sensor measurements obtained during the rise were used as inputs into a biomechanical model of each subject, and each mode of rise was evaluated based on key biomechanical metrics extracted from this model relating to stability, knee effort reduction, and rise trajectory. In addition, a questionnaire was administered to determine subjective response to and preference for each rise type.

Results show that the seat and waist assists provide statistically significant improvements in terms of stability and knee effort reduction, while the arm and bar assists do not provide any biomechanical improvement from the unassisted rise. The assists most preferred by the subject were the seat and bar assists. Because of subject preference and biomechanical improvements, of the modes tested, the seat assist was determined to be the best mode of providing assistance with sit to stand.