You breath would be gasping and your heartbeat fast. You would not be able to relax well.
You can do void meditation during the activity through total focus on it. This is described at the end of jos page about void meditation. It is the "advanced void meditation".
Controlling your mind and doing things such as void meditation during stressful activities and uncomfortable states will enable you more. Doing this in time will give you ability to control yourself during emergencies and much more. It is very good.
Void can, and should, be practiced at any time, in any situation. This will help train the mind to focus fully and at its best in emergencies, stressful situations, unexpected situations, and so on.
As naked pluto said, it is a bit more advanced thing to do void meditation after a hard day or after a stressed situation, but at some point it should be practiced.