Joséphine
Initial thoughts: A few days ago, I read The Sleep Solution by W. Chris Winter. In his book, Winter maintained that locking ourselves down to 90-minute sleep cycles isn't always efficient and might even rob us of that extra hour of sleep we need, increasing our tiredness during the day. Whose advice then, should I follow? Nick Littlehales, the author of this book, Sleep, or Winter, who's a neurologist? Both authors research sleep but I'm more inclined to trust the the trained scientist of the nervous system. Provenance matters when you want to ensure you learn the right things.
Beyond the disagreement over breaking down sleep into 90-minute chunks, Sleep was an informative book with very concrete guidelines to follow. Lots of details were included down to ideal sleeping positions and room temperatures, which makes this book a great read for anyone who's struggling with their sleep cycles and wants to achieve optimum performance, athletic or otherwise, as well as improve their health.