Kelly Starrett is a CrossFit trainer, physical therapist, author, and speaker. Wikipedia
Source: "An incredible book." - Laird Hamilton
Source: "Brilliant, brilliant, brilliant." - Kelly Starrett
Source: One of Kyle Maynard's 3 answers to "what is the book (or books) you’ve given most as a gift?"
Source: "Fantastic." - Kelly Starrett
Source: Kelly Starrett recommended this book in the "Tools of Titans" book.
Source: "[Kelly Starrett] is a legitimate fantasy and sci-fi nerd. He knows [this book] inside and out." - Tim Ferriss