Smiling while you run may increase endurance and improve performance. Exercise scientists have known for a while that your endurance hinges greatly on psychological factors along with physical ones, and that perceived effort has a big effect on performance. In general, the less effort we feel we are using, the better our performance. However, for the first time, these known facts were taken to an even more specific level in a study that tested how manipulating your facial expression while running would affect your endurance. The study, which was conducted on 24 club-level runners, showed that they used 2.8 percent less energy when smiling than frowning and 2.2 percent less energy when smiling than when they had neutral facial expressions. It follows the idea of embodied emotion, which says your facial expression can affect how you feel. There is still a question as to why, but the results as of now suggest that smiling during your workout is definitely worth a try to increase your endurance – and feel better while you do it.