How many carbohydrates are required to run a sub 2-hour marathon? | #32 ft. Dr. Robert Jacobs

In this conversation, Dr. Robert A. Jacobs and I discuss his recently accepted paper on carbohydrate oxidation and performance in sub-2 hour marathons. We explore the role of fuel utilization, the impact of exogenous carbohydrate intake, and the limitations of respiratory exchange ratio (RER) as a measurement. We also discuss the importance of training the gut and the balance between carbohydrate intake and training. The conversation touches on the differences between elite athletes and the general population, as well as the definition of health and fitness. The conversation explores the differences between running and cycling, the importance of watts per kilogram versus absolute power, the relationship between VO2 max and performance, the impact of weight on performance, the role of body fat percentage in performance, the significance of mitochondria in overall health and performance, the concept of critical power and critical oxygen, and the axis of oxidation as a key factor in performance. TAKEAWAYS 1) Fuel utilization and carbohydrate oxidation play a crucial role in endurance performance, particularly in sub-2 hour marathons. 2) Exogenous carbohydrate intake can enhance performance, but there is a saturation point beyond which absorption is limited. 3) Training the gut is important for athletes to prevent gastrointestinal distress during exercise. 4) Running up a hill engages similar muscles as cycling, making it a valuable training exercise for cyclists. 5) Absolute power is more important for flat courses, while watts per kilogram becomes a stronger predictor for uphill courses. 6) VO2 max is a valuable measure, but other factors such as threshold and efficiency also play a role in performance. 7) The axis of oxidation, referring to the role of mitochondria in cellular energy production, is a key factor in performance. Dr. Jacobs Paper - https://journals.physiology.org/doi/full/10.1152/japplphysiol.00521.2023 Enjoying these podcasts? Don't forget to subscribe to get notified when new episodes are released. If you have a question or topic you want us to address, leave a comment! Follow Phil on Instagram - https://www.instagram.com/criticalo2 Interested in testing, courses, or other long form content check out the critical oxygen website - https://www.criticaloxygen.com CHAPTERS 00:00 Introduction and Paper Acceptance 01:06 Interest in Fuel Utilization 03:56 Research Project on Carbohydrate Oxidation 08:39 Role of Carbohydrate and Fat Oxidation in Sub-2 Hour Marathon 09:22 Effect of Exogenous Carbohydrate Intake on Fat Oxidation 13:45 Limitations of RER as a Measurement 17:19 Higher Exogenous Carbohydrate Intake for Female Athletes 18:38 Carbohydrate Intake and Oxidation in the Study 19:38 Impact of Increased Carbohydrate Intake on Performance 21:24 Saturation Point of Carbohydrate Absorption 22:28 Factors Affecting Gastrointestinal Distress 25:21 Training the Gut 26:41 Balancing Carbohydrate Intake and Training 28:22 Elite Athletes and Peak Human Performance 30:08 Comparing Physical and Intellectual Abilities 32:46 Defining Health and Fitness 35:24 Acceptable Speed for Running a Mile 37:51 Measuring Mechanical Output in Running 38:38 Calories Burned While Running 40:02 Power Output in Running Uphill 41:09 Running vs Cycling 47:36 Watts per Kilogram vs Absolute Power 51:07 VO2 Max and Performance 53:16 Weight and Performance 56:09 Body Fat Percentage and Performance 59:26 Mitochondria and Performance 01:02:54 Critical Power and Critical Oxygen 01:05:13 The Axis of Oxidation