The effects of unilateral grab rail assistance on the sit-to-stand performance of older aged adults Damien M. O’Meara * , Richard M. Smith School of Exercise and Sport Science, Faculty of Health Science, The University of Sydney, P.O. Box 170, Lidcombe NSW 2141, Australia Available online 3 February 2006 Abstract This study investigated the effects of unilateral grab rail assistance during the sit-to-stand transfer to develop an understanding of lower limb joint mechanics and whole body movement patterns. External reaction forces at the grab rail and floor interfaces were also investigated to understand the nature of the assistance provided by the introduction of unilateral upper body assistance. While 12 older aged adults performed the sit-to-stand, three-dimensional body segment kinematics were recorded to determine lower body joint motion and whole body centre of mass motion. Grab rail reaction forces and bilateral ground reaction forces were recorded to determine external reaction forces and lower body joint kinetics. Grab rail assisted conditions were compared with unassisted transfers. During grab rail assistance, a systematic asymmetry was introduced to lower limb joint kinetics, without noticeable alterations to peak lower body joint motion and whole body movement patterns. Ipsilateral net joint moments and powers decreased in the ankle and hip and increased in the knee, while the contralateral net joint moments and powers increased in the hip and decreased in the knee. Joint kinetic and kinematic responses suggest a motor control strategy that maintains sym- metric sit-to-stand movement patterns by adjusting bilateral muscle control when a unilateral exter- nal reaction force is provided. Understanding the mechanical assistance that is generated during the sit-to-stand will facilitate optimal design of grab rails for older aged adults and may contribute to design for specific pathologies. Such design implementation will influence the ability of older aged adults to remain independent in the community. Ó 2005 Elsevier B.V. All rights reserved. 0167-9457/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.humov.2005.11.003 * Corresponding author. Tel.: +61 2 93519965; fax: +61 2 93519204. E-mail address: d.omeara@fhs.usyd.edu.au (D.M. O’Meara). Human Movement Science 25 (2006) 257–274 www.elsevier.com/locate/humov