Dual-Task Walking Cost in Healthy Aging: Gait Variability, Cognitive Load Allocation, and Fall Risk Stratification Across Seven Decades

This study investigates age-related dual-task walking cost in stride time variability and cognitive performance, and utility of dual-task cost as fall risk stratification marker across healthy adults aged 20-84 within the context of gerontology and human movement science, an area of growing scientific importance given its implications for fall risk screening protocol using dual-task assessment, dual-task training intervention target identification, and cognitive-motor reserve assessment in aging. Using instrumented GAITRite walkway (stride time, length, variability), digit span backward (cognitive task), and dual-task cost calculation as (single-task - dual-task)/single-task x 100; 12-month prospective fall follow-up via monthly diary, we examine increased cognitive-motor resource competition in aging as prefrontal executive control capacity declines, requiring greater attentional resources for gait stability and leaving less capacity for concurrent cognitive tasks — a capacity-sharing dual-task cost in 420 community-dwelling healthy adults (60 per decade: 20-29, 30-39, 40-49, 50-59, 60-69, 70-79, 80-84) with 12-month fall diary follow-up (84.2% retention) drawn from Nordic Aging Research Institute gait laboratory with GAITRite 6-m active area and tablet-based digit span task during walking condition. Results indicate that dual-task gait cost increases linearly from 4.2% (age 20-29) to 28.4% (age 80-84); dual-task cost >18% predicts 12-month falls with AUC 0.78, sensitivity 72.4%, specificity 78.4%; each 10% increase in dual-task cost associated with OR 2.84 for any fall (p < 0.001), with DT cost 4.2% to 28.4% across 7 decades; AUC 0.78 for fall prediction at >18% threshold as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to gerontology and human movement science and carry actionable implications for the design of programs and policies targeting fall risk screening protocol using dual-task assessment, dual-task training intervention target identification, and cognitive-motor reserve assessment in aging.