To be in good physical shape is important during a chess game. Although a lot of people claim that chess cannot belong to the class of activities known as "sports", it is clear that a chess game with a classical time control requires a big physical effort from both players. Your body will be under a big mental pressure and you have to be fully focused, sometimes twenty or thirty minutes in a row. You will sweat and your pulse will rise. To stay focused, you need to have a constant energy supply and to keep pumping fresh oxygen to your brain. Therefore, being in good physical shape helps to stay focused and to endure the pressure during a match.