Terrific book by a terrific man!... I have owned the X3 System for over a year now... I can do things now that I couldn’t do when I was 20... and I am not 20 anymore😉... Perfect training system for Martial Arts... all the strength and flexibility benefits💪... and none of the tight😤... I love watching Dr. Jaquish’s videos and articles... This book seals the deal on all the cutting cutting edge research behind Linear Variable Resistance with references... Price for this book is crazy inexpensive$$... Excellent volume from an excellent man!... Buy the book and get reading🤓... You’ll be part of the X3 family too!