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The effects of increased cognitive processing on reactive balance control following perturbations to the upper limb Trotman, Megan


While most reactive balance control studies have used whole-body perturbations, research is limited regarding how whole-body balance adjustments are integrated with continuous voluntary reaching movements when a hand perturbation is encountered. Further, when two tasks are performed simultaneously through a dual-task paradigm, performance of one or both tasks is often disrupted owing to attentional resources being divided. However, it is unclear how reactive whole-body balance responses to hand perturbations adjust when paired with a cognitive-motor task. The purpose of this study was to assess the effects of increased cognitive processing on reactive whole-body balance responses to perturbations of the hand during a continuous voluntary reaching task. Sixteen participants (8 females, 22.9 ± 4.5 years) stood and held the handle of a KINARM, a robotic-controlled manipulandum paired with an augmented visual display. Participants completed 10 trials of 100 continuous mediolateral arm movements while receiving 20 randomly interspersed anteroposterior hand perturbations throughout each trial. Participants moved their right hand at a pace of 60 beats per minute between two targets, with the hand moving towards the next target at each beat (single-task). An auditory n-back task was performed during half of the trials (dual-task), and during a quiet standing baseline trial (cognitive-motor task only). Peak centre of pressure (COP) displacement and velocity as well as time to COP displacement onset and peak following the hand perturbation were evaluated. During dual- compared to cognitive-motor task condition, n-back response times increased and percentage of correct responses decreased, indicating an increase in cognitive processing. Only peak COP displacement upon posterior perturbations during leftward reaching increased, and time to COP displacement onset upon anterior perturbations during rightward reaching decreased during dual- compared to single-task. However, there were no other differences between tasks for the remaining COP variables. Overall, there were limited differences in the COP variables during the dual- compared to single-task condition, but negative effects on the cognitive-motor task. The findings indicate that increased cognitive processing provided a minimal effect on reactive balance responses to a hand perturbation, therefore indicating balance is likely prioritized during the reaching task used here.

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