The overall objective of this project is to better understand mechanisms of age-related decrements in dual-task performance between postural control and working memory. We will specifically disentangle age-related differences in domain-specific resource limitations, as operationalized by mental versus physical fatigue, from specific central mapping-related crosstalk in modality incompatible compared to modality compatible stimulus-response mappings within cognitive-motor dual-task performance. To the authors’ knowledge, there is no study available that examined the behavioral and neural effects of physical and mental fatigue on modality-specific task interference in cognitive-postural dual-task situations in healthy young and old adults. For this purpose, two experimental series with two domain-specific fatigue interventions (physical fatigue; mental fatigue) will be launched that 1) disentangle the effects of single-mode physical (i.e., repeated sit-to-stand task until failure) and mental fatigue (i.e., attentional network test) on cognitive-postural performance during dual-task stimulus-response modality compatibility conditions in healthy young and old adults and 2) delineate brain mechanisms underlying these effects. The fatigue interventions will be coupled with modality compatibility effects and examined using procedures and outcome variables from the movement sciences and from neurocognitive psychology.