Speech as a dynamic biomarker of physical aging: a longitudinal study.

Geroscience needs biomarkers that capture the progressive decline of integrated biological systems with age. Physical capacity, a direct manifestation of systemic integrity, is a core pillar of biological aging but is typically assessed through discrete clinical tests. Speech production, a complex motor act requiring coordinated respiratory, laryngeal, and articulatory control, shares fundamental physiological pathways with global physical function and may therefore serve as an accessible digital biomarker of aging. In a longitudinal cohort of 464 community-dwelling older adults (mean age 79.6 ± 8.7 years), we tested the hypothesis that changes in speech track specific changes in physical capacity. Participants underwent a 3-month adapted physical activity (APA) program. At baseline (T0) and post-intervention (T1), we performed a battery of ten objective physical tests (strength, power, endurance, gait, balance, flexibility, mobility, appendicular lean mass, fatigue) and recorded spontaneous speech during emotional autobiographical recall. Multi-layered acoustic, temporal, and linguistic features were automatically extracted. The longitudinal association was analyzed via Spearman correlations and univariate linear mixed-effects models. The APA intervention induced significant improvements in key physical domains, including mobility, gait speed, handgrip strength, and balance (all p < 0.01). These gains were specifically correlated with concurrent changes in speech features (|ρ| = 0.11-0.22). For instance, greater lower-limb strength correlated with reduced vocal shimmer and lexical diversity, while improved flexibility was associated with a lower spectral centroid and zero-crossing rate, indicating smoother phonation. Linear mixed models confirmed significant within-individual coupling between trajectories of physical function and speech dynamics. Emotional context systematically modulated these associations, revealing different speech-stress signatures under cognitive-affective load. This study provides novel longitudinal evidence that speech is a dynamic digital biomarker of domain-specific physical capacity, reflecting underlying functional integrity. The domain-specific speech-physical coupling suggests that speech analysis can serve as a novel, integrative tool for remote monitoring of aging trajectories and the functional efficacy of interventions targeting the age-related physiological decline.