Physiological factors that can significantly impact your game
Your heart rate and adrenaline have an impact on your performance. As a chess player, understanding and monitoring various physiological aspects can have a significant impact on your performance. When you play chess, you may not be as physically active, but the mental demands of the game can still trigger an extreme stress response in your body. As was demonstrated in last month's Armageddon tournament in Berlin.
Source: chessbase.com