Heart rate and energy expenditure during extravehicular activity at different times of day

This study focuses on the comparison of heart rate during extravehicular activity (EVA) at day and night hours. Heart rate was higher during night hours than day hours, which could be explained by the additional psychological and physiological challenges of the night work accompanied by a natural decrease in the ability to work. These challenges could possibly lead to the development of a higher level of psychological tension while performing EVA during night hours in comparison with day hours, which appeared as the night increase in heart rate. The correlation analysis showed that the relationship between heart rate and physical loading (which was estimated as the level of energy expenditure) at day was different than at night. This correlation was positive at day and negative at night. It is possible that the role of heart rate increased during a rise of the cardiac output at daytime, and the input of the stroke volume increased at night, which could entirely support cardiac output at least at minimal loading. © 2015, Pleiades Publishing, Inc.