I disagree with this notion. A large component of Step I is physiology. A good understanding of physiology will also help you with understanding the more clinically related classes like pathology and pathophysiology. If you were a student who just got by meaning 70-80% in your classes, I would strongly encourage you to read physiology and biochem over the summer. It will help when you review those concepts again in the Spring of you MSII when prepping for the boards. If you were someone who did well in their classes, then I wouldn't worry so much about studying over the summer since it will just be a matter of review for you.