Difficulties in standing up and sitting down can greatly impact the quality of life of older adults. Robotic rollators equipped with moving handles can provide support to prolong the ability to live independently. However, appropriate trajectories are still unknown while the corresponding human-machine interaction dynamics are poorly understood. This study proposes bio-inspired, easy-to-implement assistance trajectories and investigates their biomechanical effects on standing-up and sitting-down motion in 15 young adults using moving handles of a robotic assistance device in a motion capture lab. The results show that moving-handles assistance can provide up to twice as much vertical support as fixed handles while potentially reducing lower and upper limb muscle demands, and reducing the destabilizing effect of horizontal forces on the handles. Furthermore, participants’ perception of provided help correlates well with the magnitude of the vertical force support. The study’s subsequent phase comprises the ongoing evaluation with frail older adults.