Abstract
Heart rate variability (HRV) is a well-established non-invasive marker of autonomic cardiac control. We test whether time spent sitting (negatively) versus lying (positively) influences vagal HRV outcomes. HRV (10-min supine electrocardiogram) and free-living postures (dual-accelerometer configuration, 7-d) were measured in 31 young healthy adults (15♀, age: 23±3). Habitual lying (66±61 mins/day), but not sitting time (558±109 mins/day), total sedentary time (623±132 mins/day), nor step counts (10752±3200 steps/day; all, p>0.090) was associated with root mean square of successive cardiac interval differences (ρ=-0.409,p=0.022) and normalized high-frequency HRV (ρ=-0.361,p=0.046). These findings document a paradoxical negative impact of waking lying time on cardioautonomic innervation.
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