The influence of sport-related concussion history on standing balance during upper limb movements under varying attentional demands.

Sport-related concussions can influence athletic performance and everyday function. We implemented a dual-task paradigm whereby perturbed reaching while standing was combined with a simple reaction-time task. The purpose was to explore how concussion history influences balance control with and without external arm perturbations under varying attentional demands. Male athletes with no previous concussions (H; n = 16; 19.3 ± 1.6 years) or history of two or more concussions (H; n = 16; 19.5 ± 1.8 years) participated. Participants reached to visual targets with their dominant hand and received randomly interspersed perturbations, performed either in isolation or simultaneously with a button press task with the non-dominant hand. Assessments included center of pressure (COP) parameters, hand movement reaction time and kinematics, and button-press reaction time. Participants with multiple concussions exhibited larger peak COP displacements and velocities than those with none. Compared to single task, the dual task increased cognitive processing and divided attention for both groups, demonstrated by slower button press and reaching reaction times, reduced anteroposterior hand velocity, and increased mediolateral hand displacement and velocity. Athletes with a concussion history likely have worse balance control, possibly owing to sensorimotor processing deficits or increased neural time delays leading to a subsequent reduction in motor activation. Because COP responses were overall maintained during the dual task, attentional resources were likely allocated towards maintaining balance control at the expense of upper limb performance.