Effect of dual tasks on gait variability in walking to auditory cues in older and young individuals.

Rhythmic auditory cues aim to modulate step times while walking. Their effect on the variability of minimum foot clearance, which is "normally" the most controlled gait parameter in normal overground walking, has not been studied, yet. We aim to analyse the effects of auditory cues on the variability of foot clearance versus the variability of other gait parameters. We further ask how the control of minimum foot clearance behaves in walking with rhythmic cuing while cognitive gait control mechanisms of higher centres is reduced through a cognitive load. Twenty young and twenty older individuals performed 4 walking conditions: normal unconstrained walking with preferred walking speed, walking with constrained step times, walking with a cognitive dual task and walking with constrained step time and a cognitive dual task. To collect kinematic gait data, we used inertial sensors which were attached to each of the subjects' feet. Gait variability was quantified using the coefficient of variation of stride time, stride length and minimum foot clearance. We did not find any differences between old and young in the variability of minimum foot clearance across all conditions, whereas in the other gait parameters, we found differences. Further, between normal walking and walking to auditory cues, we found interaction effects in the coefficient of variation of stride time and stride length, indicating a higher variability in walking on metronome beats in older people. Interaction effects were reverted when additionally to the auditory cuing a cognitive dual task had to be solved. Our findings show that contrary to findings in patients with neurological disorders, synchronizing stepping to rhythmic auditory cues increase stride time variability but not the variability of minimum foot clearance in healthy older adults. This effect might be due to an imposed intrinsic focus which negatively influences motor performance. Shifting this focus towards a cognitive task seems to normalize the variability of gait parameters in older individuals.