Not All Sitting Is Equal in Later Life: A Perspective on Cognitively Active Sedentary Behavior

Sedentary behavior is conventionally defined as waking time spent sitting, reclining, or lying at very low energy expenditure (≤1.5 METs), a definition that supports surveillance and guideline translation. For cognitive and mental-health outcomes in later life, however, total sedentary minutes may be too coarse: seated episodes differ in cognitive demand, social context, autonomy over pacing, and stopping cues. This perspective advances a falsifiable thesis: distinguishing cognitively active from cognitively passive sedentary domains should yield more coherent and interpretable associations with cognition and mental health than total sedentary time alone. Existing evidence suggests that passive, media-dominant patterns and cognitively engaging seated practices relate differently to cognitive decline, dementia risk, and depression-related outcomes, although confounding and reverse causality remain central concerns. We propose a minimal measurement agenda: domain reporting, key modifiers, reliability flags for mixed episodes, episode-linked ecological momentary assessment, and time-reallocation contrasts. If domain resolution does not improve stability, coherence, or substitution-based interpretability, the thesis should be rejected or revised.