Your Body's Three Engines (And How to Train All of Them)

You've probably felt the burn at the end of a hard interval and the dead legs at mile 22 of a marathon. Both are painful, but they're completely different kinds of suffering, and they come from different energy systems inside your body. In this episode, Coach Brad breaks down the three energy systems that power every run you do: the phosphagen system, the glycolytic system, and the oxidative system. Using a simple three-gear transmission analogy, he explains what each system does, what it feels like when it's working (and when it's failing), and which workouts in your training plan target each one. You'll also learn why the old "lactic acid causes the burn" myth is wrong, what's actually happening when you hit the wall in a marathon, and why your easy runs might be the most important runs in your entire training plan. In This Episode Why your body's three energy systems are like a car with three gears The phosphagen system and why even marathoners need to train it What's actually causing the burning sensation during hard efforts (it's not lactic acid) How Dr. George Brooks' research flipped decades of conventional wisdom on lactate Why tempo runs are one of the most valuable workouts for distance runners The oxidative system and why it's the engine distance runners live and die by The cellular adaptations that happen when you build your aerobic base How to map every workout in your training plan to a specific energy system Why running your easy runs too fast puts you in a training no man's land The real reason runners hit the wall (and it's not a lack of mental toughness) Key Takeaways All three energy systems run simultaneously. There's no light switch between them. One system is always dominant, but the others are always contributing. Lactate is a fuel, not a waste product. The burn you feel during hard efforts comes from hydrogen ions, not lactate. Lactate actually helps buffer that acidity. Tempo runs widen your lactate-clearing pipeline. Training at or near your lactate threshold improves your body's ability to shuttle and recycle lactate, letting you sustain faster paces for longer. Your aerobic base is built at the cellular level. Consistent easy running increases mitochondrial density, capillary density, stroke volume, and fat-burning efficiency. These changes take months to build, which is why patience with base training pays off. Every workout should have a clear purpose. Easy runs build your aerobic engine, tempo runs train lactate clearance, intervals challenge your glycolytic system, and sprints sharpen neuromuscular coordination. When you understand the why, training becomes purposeful instead of random. Timestamps 00:00 - The 5K Kick vs. the Marathon Fade 02:34 - What Is ATP and Why Your Body Has Three Ways to Make It 04:51 - The Three-Gear Transmission Analogy 05:48 - Engine #1: The Phosphagen System (Your Rocket Booster) 08:51 - Engine #2: The Glycolytic System and the Burn 10:12 - Why Everything You've Heard About Lactic Acid Is Wrong 13:59 - Engine #3: The Oxidative System (Your Endurance Engine) 16:38 - What Aerobic Training Does at the Cellular Level 18:28 - Mapping Your Workouts to Each Energy System 21:35 - Why Runners Hit the Wall (And How to Prevent It) 24:53 - Wrap-Up and the VMAX App References Brooks, G.A. (2018) – "The Science and Translation of Lactate Shuttle Theory" – Key research establishing lactate as a fuel source, not a waste product Rapoport, B.I. (2010) – "Metabolic Factors Limiting Performance in Marathon Runners" – Research on glycogen depletion and hitting the wall Dr. Otto Meyerhof – 1920s research on frog leg muscle stimulation and the original (now-corrected) lactate/fatigue hypothesis Connect With VMAX Website: vmax.run Instagram: @vmax.running Thanks for listening! If you enjoyed this episode, please leave a review and share it with a running buddy who could use a better understanding of why every run in their plan matters.