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How to determine your maximal sustainable intensity (second threshold) | #21 ft. Dr. Robert Jacobs

Updated: Jan 31

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This episode of the Critical Oxygen podcast discusses the concept of thresholds in exercise physiology. Dr. Robert Jacobs and I explore the confusion surrounding thresholds and the various ways they are measured. We also discuss the limitations of lactate testing and the disconnect between research and real-world application. The practical application of thresholds in training and competition is explored, as well as their relevance for beginners. The episode concludes with a discussion on the critical power model and its implications for sustainable exercise intensity.


1) Second threshold is used to define the delineation between sustainable and unsustainable exercise intensity.

2) Lactate testing has limitations and should be used in conjunction with other measures.

3) Practical application of thresholds in training and competition requires individualization and a focus on pacing.

4) Critical power is a mathematical model that represents the maximum sustainable power output an individual can maintain for an extended period of time.

5) The critical power model has limitations and may overestimate an individual's sustainable power output.

6) Consistency in testing and measuring physiological variables is crucial for tracking changes in performance.


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00:00 Introduction to Thresholds

03:22 Confusion around Thresholds

08:20 Thresholds and Exercise Duration

13:09 Limitations of Lactate Testing

17:06 The Disconnect between Research and Real-World Application

19:26 Maximal Lactate Steady State

22:47 Steady State Isn't Steady

26:32 Practical Application of Thresholds in Training

34:13 Thresholds in Competition

41:33 Thresholds for Beginners

44:28 The Critical Power Model

50:19 Understanding Critical Power

51:45 Challenges of Maintaining Critical Power

52:18 Factors Affecting Critical Power

56:30 Physiological Models for Performance

57:25 The Impact of Hydration and Nutrition

59:16 Individual Variability in Performance

01:01:13 Optimizing Training Zones

01:04:32 Performance as a Sine Wave

01:06:29 Limitations of the Critical Power Model

01:07:16 Caveats of Time to Exhaustion Trials

01:08:14 Alternative Testing Methods

01:09:13 Consistency in Testing

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