1) “Peak Performance” by Brad Stulberg and Steve Magness.
This is at the top of my list right now. It is packed with research and is written so that it is easy to follow and understand. Whether you are an athlete or not, there are lessons relatable to all humans trying to improve in anything at all. The overarching theme of this book is, “stress plus rest equals growth”. Seems pretty simple, but most of need work on the rest part of this equation.