We welcome back Dr. Phil Skiba to the show to discuss his latest book, "Scientific Training for Endurance Athletes," and in particular his work with Critical power/W Prime. W Prime (also known as Anaerobic Work Capacity), is the amount of work you are able to do above your Critical Power (CP) and is measured in joules (J) or kilojoules (KJ). A world-renowned expert in elite athletic performance, Dr. Philip Skiba is the Medical Director of Sports and Musculoskeletal Medicine for Advocate Aurora Health, where he leads both the Human Performance and Biomechanics Laboratories. He is also the head primary care sports physician for the NCAA Division 1 University of Illinois – Chicago (UIC). He has extensive experience in covering mass-participation events, including the NYC and Chicago marathons, ITU Triathlons and the Soldier Field 10-Miler. Dr. Skiba has personally trained a number of Olympian, national champion and world champion athletes, including world-record holders. His work on the mathematics of high-intensity exercise (The W′Balance Model) has fundamentally changed how scientists and coaches prescribe and analyze interval training and race strategy. Recruited to the Nike Breaking 2 project, Dr. Skiba worked with 3 of the fastest runners on the planet in pursuit of the sub-2-hour marathon. He appeared in and narrated the Cannes award-winning National Geographic documentary Breaking 2. Dr. Skiba serves on the medical board of USA Cycling, and is a Fellow of the American College of Sports Medicine. He has academic appointments at both UIC and the University of Exeter (UK). In this episode we explore the significance of understanding the threshold between stable and unstable physiology, especially in relation to endurance sports like running and cycling. Critical speed or power serves as a marker for this threshold and exceeding it taps into a finite energy reserve conceptualized as W prime. Managing this energy is crucial for race strategy, determining when to make an effort and how long it can be sustained for. We discuss the critical power W prime model and its importance in training over traditional FTP workouts. We consider training strategies for both novice and seasoned athletes, highlighting the benefits of base training and fatigue resistance before moving on to threshold and interval work. For experienced athletes, we discuss a reverse periodization approach to training. We explore the nuances of training for long-distance triathlon, focusing on how manipulating W prime and critical power can optimize performance. We share insights on the importance of tailoring interval sessions to an athlete's individual capacity, particularly for those with a smaller W prime who may struggle with standard VO2 intervals. Lastly, we explore the benefits of using GPS and power meters for monitoring athlete performance, noting the advantage of having concrete data during training and competition, and we address the increasing challenges in professional sports, including the issue of doping and its impact on clean athletes. LINKS: Follow Dr Skiba on Twitter on https://twitter.com/DrPhilipSkiba Scientific Training for Endurance Athletes at https://www.amazon.com/Scientific-Training-Endurance-Athletes-Philip/dp/0979463629/ International shipping site at http://shipitto.com/ Dare to Tri at https://dare2tri.org/