There's an old saying, "All work and no play makes Jack a dull boy." Like Jack, without body breaks from work and times of physical activity, your child will become very dull too, unable to focus and continue learning effectively. So why not schedule body breaks and physical activity right into your day? It doesn't need to be a large amount of time, 10-20 minutes will do wonders. It could be a simple as setting a timer and when it goes off, everyone does jumping jacks or runs up and down the stairs or goes for a walk around the block - anything to get up, get active, and get moving! Everyone will be happy for the change and more able to get back to work afterwards.
What breaks and physical activity are you scheduling today?