Effects of age in a cognitive-motor dual task: parametric manipulations of cognitive load and motor difficulty

Everyday mobility requires the continuous allocation of limited executive resources between cognitive and motor control. Prioritization theory predicts that biomechanical stability is prioritized as load increases to reduce fall risk. Although dual-task walking has been widely studied, most investigations examine the kinematic effects of a single cognitive task on a single walking condition, providing limited insight into how cognitive-motor interactions evolve as task demands progressively increase. Here we examined how increasing cognitive load and motor difficulty jointly influence gait adaptation in healthy younger and older adults.

Younger (n = 29) and older adults (n = 30) performed auditory 0-, 1-, and 2-back tasks while walking on a treadmill at three inclines (level, intermediate, highest). Working memory performance and gait kinematics were analyzed.

Increased cognitive load produced declines in d' and increases in RTs. Both age groups showed similar increases in RT with increased load, but older adults exhibited greater decreases in d' with increased load. Age-related gait differences were observed, especially with increases in motor difficulty, but they were parameter-specific, concentrated in stride length, stride frequency and toe clearance rather than reflecting a uniform age-related decline across all gait measures. Compared with younger adults, older adults' gait was characterized by lower toe clearances, higher stride frequencies, shorter relative stride lengths, and greater time in double support. As motor difficulty increased, younger adults progressively adapted their gait across all incline levels, whereas older adults made these adaptations only between the lowest and higher inclines. RT and d'-both presumed to reflect executive function-were related to gait in qualitatively different ways. RT was generally associated with gait parameters, while d' was highly specific to incline, and in one case, task difficulty.

These findings support capacity-sharing and posture-first accounts of cognitive-motor interaction. In addition to age-related baseline differences, executive function explains additional variance in adaptive gait responses under increasing task demands.