Lower limb exoskeletons for older adults: key assistance parameters and evaluation of ankle assistive strategies via musculoskeletal modelling.

Aging comes with physiological changes resulting in alterations to gait, decline of muscle function, and balance that contribute to reduced mobility, increased metabolic cost of walking, and elevated fall and injury risks in older adults. Wearable lower-limb exoskeletons have emerged as a promising strategy to support healthy aging; however, identifying optimal assistance strategies remains challenging due to the complexity and cost of experimental testing. In this study, we combined musculoskeletal modelling and simulations to identify key assistance parameters for older-adult gait and evaluate different ankle exoskeleton configurations computationally, based on muscle activation, metabolic consumption, device weight and power requirement, efficiency, and performance. Motion capture, force plate, and electromyography data from younger and older adults were processed using OpenSim-based musculoskeletal simulations with age-adjusted muscle parameters. Age-related gait differences were quantified across spatiotemporal, kinematic, kinetic, and muscle activation metrics. Subsequently, unilateral and bilateral ankle assistance strategies providing plantarflexion (PF), dorsiflexion (DF), or combined plantarflexion-dorsiflexion (PFDF) support were simulated using unidirectional path actuators representative of cable-driven exoskeletons. Older adults exhibited reduced ankle and hip range of motion, decreased plantarflexion, delayed joint moments, shorter step length, and increased double support time compared with younger adults. These changes suggest that elderly gait can be improved with kinematic assistance at the ankles and hips, timed kinetic assistance at the knees and hips, as well as balance support, hence an opportunity for exoskeleton intervention. Simulated ankle assistance reduced muscle activations and metabolic expenditure, with bilateral PFDF assistance providing the greatest overall benefits. While dorsiflexion-only assistance reduced power requirements, it occasionally increased metabolic consumption. Overall, bilateral assistance outperformed unilateral configurations across most performance metrics. These findings provide biomechanical design guidelines for future lower-limb exoskeletons targeting mobility enhancement and fall-risk reduction in aging populations and demonstrate the value of computational biomechanics for screening assistive-device configurations prior to experimental implementation.