Predictive neuromechanical simulations indicate why walking performance declines with ageing

Abstract

Key pointsr Although the natural decline in walking performance with ageing affects the quality of life of a growing elderly population, its physiological origins remain unknown.r By using predictive neuromechanical simulations of human walking with age-related neuro-musculo-skeletal changes, we find evidence that the loss of muscle strength and muscle contraction speed dominantly contribute to the reduced walking economy and speed.r The findings imply that focusing on recovering these muscular changes may be the only effective way to improve performance in elderly walking.r More generally, the work is of interest for investigating the physiological causes of altered gait due to age, injury and disorders.Abstract Healthy elderly people walk slower and energetically less efficiently than young adults. This decline in walking performance lowers the quality of life for a growing ageing population, and understanding its physiological origin is critical for devising interventions that can delay or revert it. However, the origin of the decline in walking performance remains unknown, as ageing produces a range of physiological changes whose individual effects on gait are difficult to separate in experiments with human subjects. Here we use a predictive neuromechanical model to separately address the effects of common age-related changes to the skeletal, muscular and nervous systems. We find in computer simulations of this model that the combined changes produce gait consistent with elderly walking and that mainly the loss of muscle strength and mass reduces energy efficiency. In addition, we find that the slower preferred walking speed of elderly people emerges in the simulations when adapting to muscle fatigue, again mainly caused by muscle-related changes. The results suggest that a focus on recovering these muscular changes may be the only effective way to improve performance in elderly walking.

Predicting gait adaptations due to ankle plantarflexor muscle weakness and contracture using physics-based musculoskeletal simulations

“…Researchers have created controllers that could generate various gait patterns, including level walking [20-23] and running [21,23], inclined walking [22,23], loaded walking [22], stair ascent, and turning [23]. More recently, Song and colleagues sought to understand which factors contributed to decreased walking performance in the elderly population [24]. By systematically introducing the neural, muscular, or skeletal deficits seen in this population and training each model to walk, they determined that decreased muscle strength and mass of all muscles contributed…”

“…These studies suggest strong links between muscle deficits and the observed gait adaptations; however, since these studies tracked experimental data from patients with a combination of muscular, skeletal, and neural deficits, the independent effects of muscular weakness and contracture on the observed gait adaptations cannot be assessed.Simulations in which kinematics are generated de novo (i.e., without tracking experimental data) can help reveal cause-effect relationships between muscular deficits and gait abnormalities.Researchers have created controllers that could generate various gait patterns, including level walking [20-23] and running [21,23], inclined walking [22,23], loaded walking [22], stair ascent, and turning [23]. More recently, Song and colleagues sought to understand which factors contributed to decreased walking performance in the elderly population [24]. By systematically introducing the neural, muscular, or skeletal deficits seen in this population and training each model to walk, they determined that decreased muscle strength and mass of all muscles contributed…”

Walking cadence affects the recruitment of the medial-lateral balance mechanisms

“…A larger margin of stability is viewed as safer and more stable. Recent modeling results indicate that slowed gait can be explained entirely by diminished muscle strength (Song and Geyer, 2018). However, Fan et al (2016) has shown older adults with slower gait can walk faster if instructed, suggesting that locomotor capacity (i.e.…”

Simulating the Impact of Glenohumeral Capsulorrhaphy on Movement Kinematics and Muscle Function in Activities of Daily Living

“…Similar to musculoskeletal simulations, the predictive simulation approach has been more readily applied in a gait context. 17,18 Song and Geyer 18 induced neural, muscular and skeletal deficits associated with ageing to generate predictive simulations of walking in the elderly. Muscle strength and mass were subsequently identified as the predominant factors responsible for the typical gait changes seen in elderly populations.…”

“…Muscle strength and mass were subsequently identified as the predominant factors responsible for the typical gait changes seen in elderly populations. 18 Ong et al 17 simulated isolated weakness or contracture of the plantarflexor muscles to emulate adaptations in the musculoskeletal system typically observed with cerebral palsy. Muscle weakness elucidated a slower 'heel-walking' gait, while contracture resulted in a crouched 'toewalking' gait -agreeing with the common gait adaptations seen in experimental evaluations of those with cerebral palsy.…”