Differences between grab rail position and orientation during the assisted sit-to-stand for able-bodied older adults

The aim of this study was to compare the effects of grab rail position, orientation, and number of hands used on the kinetics of assisted sit-to-stand transfers. Participants were 12 able-bodied older adults between the ages of 69 and 88 years. While each one performed the sit-to-stand transfer, a motion analysis system with 9 cameras recording at 60 Hz tracked the 3-D trajectories of retroreflective markers. Bilateral 37-D platform, grab rail, and seat force data were collected at 200 Hz and normalized to participant body weight. Four lateral conditions were tested: vertical, 45 degrees inclined, and horizontal with the hand placed at 150 mm and 400 mm forward of the seat front edge. Four anterior conditions were tested: vertical and horizontal orientations with the use of one hand and two hands. Posterior grab rail force increased with anterior assistance and with two-hand use compared to lateral assistance and single hand use, respectively. The selection of grab rail position and the number of hands incorporated during assistance also determined the symmetry of anteroposterior net joint forces, net joint moments, and joint powers. Grab rail orientation determined the height of the gripping hand which influenced the assistance strategy. Grab rail position, orientation, and the amount of upper body contribution influenced the assisted sit-to-stand transfer. These kinetic responses to grab rail location require careful consideration in order to optimize grab rail assistance during the sit-to-stand transfer.