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

Updated: Feb 28


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.



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.

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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

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