Dual-Task Performance as a Potential Digital Biomarker of Aging: Age-Stratified Reference Patterns Across the Adult Lifespan.

Objectives: To characterize age-stratified reference patterns in dual-task performance and dual-task cost across the adult lifespan using a standardized digital assessment. Methods: A cross-sectional observational study was conducted in 400 healthy participants aged 18 to 94 years from Spain and Ecuador. Participants performed a digital dual-task test combining a motor task (cursor control to hit a virtual target) and a cognitive task (arithmetic operations). Performance was assessed under single-task (ST) and dual-task (DT) conditions. Dual-task cost (DTC) was calculated separately for the motor and cognitive components, together with a composite Mean DTC. Participants were grouped into seven age categories for descriptive age-stratified analyses, and differences were assessed using one-way ANOVA with Bonferroni-adjusted post hoc comparisons. In addition, multiple linear regression analyses were performed with age treated as a continuous variable and sex as a covariate. Results: Motor and cognitive performance was lower across older age groups under both ST and DT conditions. DTC differed significantly across age groups (p < 0.001), with larger differences becoming apparent at older ages. Cognitive DTC showed a marked increase across older age groups, indicating substantial age-associated cognitive interference under dual-task conditions. Mean DTC increased from 28.1% in participants aged 18-29 years to 63.2% in those aged ≥80 years. Age remained significantly associated with Motor DTC (B = 0.506 per year; 95% CI 0.422-0.589; p < 0.001), Cognitive DTC (B = 0.582; 95% CI 0.497-0.667; p < 0.001), and Mean DTC (B = 0.544; 95% CI 0.483-0.604; p < 0.001) after adjustment for sex. Although adjusted DTC levels differed between sexes, no significant age × sex interaction was observed. Conclusions: Digital dual-task performance differed substantially across age groups, with higher dual-task costs observed at older ages. These findings provide age-stratified reference data for this specific digital cognitive-motor paradigm and support its further investigation as a scalable measure of cognitive-motor interference. Further psychometric, longitudinal, and clinical validation is required before the Dualtask Test can be established as a clinical biomarker or used to distinguish physiological age-associated differences from pathological cognitive decline.