An Overview of the Effects of Experimentally Induced Fatigability on Walking in Aging and Parkinson’s Disease

One of the most important characteristics of human motor control is the ability to adapt to internal perturbations and cope with environmental situations, task constraints, and internal perturbation. Natural aging and age-related diseases, in particular, Parkinson’s disease (PD), may restrict the capacity to cope with perturbation during the performance of motor tasks, such as walking. One way of experimentally examining the ability to adapt walking to internal perturbation is by limiting the availability of internal resources through induced fatigability. Specifically, experimentally induced fatigue state by physical/muscle exercise (muscle fatigability) may reduce the neural and peripherical capacity of controlling and coordinating muscles, while mental exercise-induced fatigue state (mental fatigability) may interfere with the availability of cognitive resources involved in cognitive functions that can consequently interfere with walking performance. In this chapter, we present up-to-date research regarding age- and PD-related walking adaptation to muscle and mental fatigability. We focus on combining such effects from a perspective of fatigability task-specificity as well as different walking conditions. We discuss potential mechanisms of fatigability as an internal perturbation interfering with walking in an age- and PD-specific way and we propose a hypothetical model of those interference and associated factors (e.g., physical activity level). Finally, we discuss potential niches and needs for future studies.