The effects of cognitive loading on balance control in patients with multiple sclerosis.

The aim of this study was to compare the effects of concurrent cognitive task (silent backward counting) on balance performance between two groups of multiple sclerosis (MS) (n=23) and healthy (n=23) participates. Three levels of postural difficulty were studied on a force platform, i.e. rigid surface with eyes open, rigid surface with eyes closed, and foam surface with eyes closed. A mixed model analysis of variance showed that under difficult sensory condition of foam surface with eyes closed, execution of concurrent cognitive task caused a significant decrement in variability of sway velocity in anteroposterior direction for the patient group (P<0.01) while this was not the case for healthy participants (P=0.22). Also, the variability of sway velocity in mediolateral direction was significantly decreased during concurrent execution of cognitive task in patient group (P<0.01) and not in healthy participants (P=0.39). Furthermore, in contrast to single tasking, dual tasking had the ability to discriminate between the 2 groups in all conditions of postural difficulty. In conclusion, findings of variability in sway velocity seem to confirm the different response to cognitive loading between two groups of MS and healthy participants.