Dr. Verkuil & Dr. Brosschot from Leiden University use heart rate variability (HRV), to investigate the impact of psychological stress on physiological stress. It is therefore important to measure psychological stress at moments when people are likely physiologically stressed. In their project, all periods of HRV that are not explained by physical activity will be detected. Each non-metabolic induced HRV decrease period will trigger a smartphone app that asks subjects to indicate what they are currently thinking and doing and how they are currently feeling. The aim of this study is to test if stress cognition is increased during periods of HRV decrease compared to random neutral episodes. Leiden University realizes this highly innovative project using movisens ecgMove and movisensXS.