Can athletes fat-adapt their workouts? This lesson lays down the principles of exercise biochemistry and physiology needed to understand the importance of the three energy systems supporting energy metabolism in skeletal muscle: the phosphagen system (ATP and creatine), anaerobic glycolysis (dependent on carbs), and oxidative phosphorylation (dependent on carbs, fat, or protein). We discuss why maximal intensity always depends on carbs if the intensity and duration are sufficient to deplete phosphocreatine concentrations, and clarify the window of time and intensity that can be fat-adapted. This sets the foundation for the next lesson, which looks at the evidence of how carbohydrate restriction and ketogenic diets impact sports performance. For the full episode, go to chrismasterjohnphd.com/mwm/2/17 Sign up for MWM Pro for early access to content, enhanced keyword searching, self-pacing tools, downloadable audio and transcripts, a rich array of hyperlinked further reading suggestions, and a community with a forum for each lesson.