And now, for a new segment on the Legion podcast: “Science with Sergio” Lots of CrossFitters talk about lactate or “lactic acid,” like joggers from the 1970s—saying things like “my legs were burning with lactic acid” or “my lat are so sore from the lattice acid from that workout yesterday.” Our understanding of the metabolism of lactate has progressed quite a bit, so we wanted to dig into a paper from Iñigo San-Milán and George Brooks that gives a more detailed and accurate framing of how lactate functions in the body as a fuel source, a signaling molecule, and—in some cases—as a fatigue mechanism. On this podcast, Sergio and Todd break down “Assessment of Metabolic Flexibility by Means of Measuring Blood Lactate, Fat, and Carbohydrate Oxidation Responses to Exercise in Professional Endurance Athletes and Less-Fit Individuals.” By better understanding the in-the-weeds metabolism, we can better filter fitness snake oil and have a more accurate framework for how athletes get through conditioning—and what actually slows them down. Check out the full conversation with Todd and Sergio to learn: How elite athletes metabolize lactate How aerobic and anaerobic metabolism relate to lactate production How to practically apply this understanding of metabolism to training CrossFitters If you're not already subscribed to our newsletter, head over to www.legionsc.com to get a weekly selection of training tips and our favorite articles. You can follow us on Instagram as well for regular training tips and crunchy tactics: @legion.sc Links & Resources Mentioned “Assessment of Metabolic Flexibility by Means of Measuring Blood Lactate, Fat, and Carbohydrate Oxidation Responses to Exercise in Professional Endurance Athletes and Less-Fit Individuals” by Iñigo San-Milán and George Brooks ATP/ADP sycle Citric acid cycle Electron transport chain “Fast-Twitch Vs. Slow-Twitch Muscle Fiber Types” Show Notes: [00:13] Introduction to “Science with Sergio” and “Assessment of Metabolic Flexibility by Means of Measuring Blood Lactate, Fat, and Carbohydrate Oxidation Responses to Exercise in Professional Endurance Athletes and Less-Fit Individuals” from Iñigo San-Milán and George Brooks. [03:45] Some key foundational concepts: metabolic flexibility and fat and carbohydrate oxidation, lactate, the citric acid cycle, the electron transport chain, and aerobic vs anaerobic metabolism [12:08] Does lactate actually cause fatigue and soreness? What’s the deal with “lactate threshold”? [17:04] A breakdown of the study’s methodology and findings: elite athletes, recreational athletes, and metabolically damaged individuals all rode a bike ? [25:17] Lactate as a fuel source and why lactate both correlates with and potentially causes fatigue [35:27] How can people apply this understanding of lactate to actual performance in fitness? What is the value of Zone 2 training? How do CrossFitters do it wrong? [43:52] Why CrossFit has more complicated limiters than just mitochondrial function. [49:51] “The fat burning zone” doesn’t have anything to do with people losing weight or body fat. [53:37] Science with Sergio wrap up