Age-related interplay of walking economy, stability, and neuromuscular coordination during single- and dual-task walking

BACKGROUND: Efficient and stable walking is essential for preserving independence in older age, yet the interplay among walking economy, stability, and neuromuscular coordination, especially under cognitive-motor interference, remains unclear. This study examined age-related changes in these factors during single-task walking (STW) and dual-task walking (DTW) to determine their contributions to energetic cost. METHODS: Fifteen older adults and thirteen young adults performed STW and DTW. Net VO₂ and cost-ratio were derived from metabolic data. Whole-body kinematics and electromyography of lower-limb muscles were collected. The distance between the extrapolated center of mass and center of pressure (XCoM-CoP), sample entropy of the center of mass (CoM-SampEn), muscle synergies, and muscle networks were calculated. Partial least squares regression was used to identify multivariate determinants of cost-ratio. RESULTS: Older adults exhibited a significantly higher metabolic cost-ratio than young adults, especially during DTW. XCoM-CoP displacements increased during DTW. Older adults utilized fewer synergies alongside higher coactivation, synergy entropy, and network density during walking. PLSR indicated that during STW, cost-ratio was primarily driven by age (β = 0.347) and speed (β = -0.232). In DTW, age (β = 0.668), synergy entropy (β = 0.266), and speed (β = 0.022) emerged as the key predictors of metabolic cost-ratio. CONCLUSION: Aging is associated with simplified muscle synergies and strengthened coactivation, which helps preserve stability under cognitive load but elevates energetic cost. These findings demonstrate that cognitive interference strengthens the coupling between neuromuscular organization and energetic expenditure, identifying synergy entropy and dual-task energy cost as potential targets for monitoring and improving mobility in older adults.