Studying can be demanding and draining.  One way to stay fresh during this time is to study for approximately 15 to 20 minutes and then stop.  Get up and move around and get some water.  Water is the best drink for studying as it keeps you fresh.  Some things to do in the break periods is to stretch, walk around and be active.  The breaks should last no longer than 10 minutes.  When you go back to studying, you will find that you are refreshed and ready to continue studying.