He’s the author, co-author, or ghostwriter of a number of books, including the five-book Core Performance franchise with Mark Verstegen, who revolutionized the fitness industry with his groundbreaking Core Performance training system. Williams also collaborated with Jay Cardiello on Cardio Core 4x4 (Rodale, 2012) and with Brody Welte on Paddle Fit, a video “vook” on stand-up paddleboarding (Vook, 2011).