title: Timing of reactive stepping among individuals with sub-acute stroke: effects of 'single-task' and 'dual-task' conditions.
abstract: Performance decrements in balance tasks are often observed when a secondary cognitive task is performed simultaneously. This study aimed to determine whether increased cognitive load resulted in altered reactive stepping in individuals with sub-acute stroke, compared to a reactive stepping trial with no secondary task. The secondary purpose was to determine whether differences existed between the first usual-response trial, subsequent usual-response trials, and the dual-task condition. Individuals with sub-acute stroke were exposed to external perturbations to elicit reactive steps. Perturbations were performed under a usual-response (single-task) and dual-task condition. Measures of step timing and number of steps were based on force plate and video data, respectively; these measures were compared between the usual-response and dual-task trials, and between the first usual-response trial, later usual-response trials (trials 2-5) and a dual-task trial. A longer time of unloading onset and greater number of steps were identified for the first usual-response trial compared to later usual-response trials. No significant differences were identified between usual-response and dual-task trials. Although improvements were observed from the first to subsequent usual-response lean-and-release trials, performance then tended to decrease with the introduction of the dual-task condition. These findings suggest that when introduced after usual-response trials, the dual-task trial may represent the first trial of a new condition, which may be beneficial in reducing the potential for adaptation that may occur after multiple repetitions of a reactive stepping task. Therefore, these findings may lend support to the introduction of a new condition (i.e. a dual-task trial) in addition to usual-response trials when assessing reactive balance in individuals with stroke.
authors.affiliation: Toronto Rehabilitation Institute-University Health Network, 550 University Ave, Toronto, Ontario M5G 2A2, Canada; School of Physical and Health Education, Nipissing University, 100 College Drive, Box 5002, North Bay, Ontario P1B 8L7, Canada.
authors.forename: Alison
authors.initials: A
authors.lastname: Schinkel-Ivy
authors.affiliation: Human Health and Nutritional Sciences, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada.
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Huntley
authors.affiliation: Toronto Rehabilitation Institute-University Health Network, 550 University Ave, Toronto, Ontario M5G 2A2, Canada; Department of Physical Therapy, University of Toronto, 500 University Ave, Toronto, Ontario M5G 1V7, Canada.
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: Inness
authors.affiliation: Toronto Rehabilitation Institute-University Health Network, 550 University Ave, Toronto, Ontario M5G 2A2, Canada; Department of Physical Therapy, University of Toronto, 500 University Ave, Toronto, Ontario M5G 1V7, Canada; Evaluative Clinical Sciences, Hurvitz Brain Sciences Research Program, Sunnybrook Research Institute, 2075 Bayview Ave, Toronto, Ontario M4N 3M5, Canada.
authors.forename: Avril
authors.initials: A
authors.lastname: Mansfield
keywords: Health sciences; Medicine