Mechanisms of postural stabilization in younger and older people during rapid transitions in the direction of voluntary sway

Abstract

Age-related declines in postural control are well described, however little is known about how the elderly control stability during challenging postural tasks. Experiment 1 examined age-related differences in reaction time (RT) and coordination between centre of pressure (COP), trunk and head motion during rapid transitions of sway between the AP and ML directions. Compared to the young, older participants exhibited slower RT and stronger coupling between COP, trunk, and head motion during both the initiation and execution of the sway transition. Experiment 2 aims to determine how these altered coordination responses of the elderly impact on stability. Particular emphasis will be placed on examining excursions of the COP with respect to the centre of mass (COM). 3D marker positions (VICON full body plug-in gait model), force plate, and leg muscle EMG data was collected from 25 younger (age = 25 ᠴ years) and 51 older (age = 76 ᠶ years) men and women. Participants either initiated AP or ML sway from quiet stance, or orthogonally switched sway between the AP and ML directions. Variables extracted from the current data analysis include horizontal COP-COM distance, strength of COP and COM coupling, COP and COM velocity, and minimum time-to-contact of the COP and COM with the base of support limit. It is hypothesized that compared to the young, older participants controlled stability differently during the sway transitions as reflected in the COP/COM measures.