Effect of cognitive and motor dual-task on stability and variability of walking in younger and older adults

Dual-task walking, performing a secondary task while walking, challenges attentional and motor resources and has been linked to increased fall risk. While cognitive dual tasks are most often studied, physical (e.g., load carriage) and "combination" tasks such as obstacle crossing may also impact gait. Whole-body angular momentum and its variability provide sensitive markers of locomotor stability. We investigated how dual-task type influences gait mechanics and stability in younger and older adults. Sixteen adults (18-80 years) completed four treadmill conditions at preferred walking speed: baseline walking (PWS), walking while talking (WWT), box carriage (BOX, 15 lb), and obstacle crossing (OBS). Spatiotemporal measures, trailing limb angle (TLA), and whole-body angular momentum in frontal and sagittal planes were computed. Mixed-model ANOVAs and statistical parametric mapping assessed trial and age effects. Dual tasks altered spatiotemporal gait. BOX and OBS reduced step length, and OBS also shortened step time and reduced late-stance TLA. OBS elicited consistently greater variability in step length, width, time, double-support, and whole body angular momentum in both planes (all p < .01). Older adults took shorter steps and longer double support, with age × task interactions observed in these metrics. Obstacle crossing imposed the greatest locomotor challenge, producing significant changes in TLA, whole body angular momentum, and variability, whereas cognitive and load carriage tasks induced smaller deviations. Findings highlight the importance of incorporating ecologically relevant "combination" tasks into gait assessment and demonstrate the utility of time-series analyses for detecting phase-specific disruptions to locomotor stability.