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Is the Best Predictor of Endurance Performance your Muscle?! | #13 ft. Dr. Robert Jacobs

Updated: Jan 31

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In this episode, Dr. Robert Jacobs and I discuss remote physiology testing and its potential to optimize training. We also delve into the importance of predictors of performance, such as mitochondrial function and capillary density. The conversation includes a review of a research study we conducted on traditional predictors of performance and their correlation with endurance performance. The episode concludes with a discussion on the calibration and cuffing protocol used in the study and its validation. This conversation explores the measurement of skeletal muscle oxygenation and its correlation with performance. The importance of oxygen delivery and utilization in performance is emphasized.


Remote physiology testing offers a convenient and affordable way to optimize training.

Mitochondrial function and capillary density are important predictors of endurance performance.

Traditional predictors of performance, such as VO2 max and efficiency, may not be as accurate as previously thought.

The cuffing protocol has been validated and shows a strong correlation with endurance performance.

Skeletal muscle oxygenation is an important factor in performance, with the balance between oxygen delivery and utilization playing a key role.

Mitochondria play a central role in energy transduction and are crucial for performance and overall health.

Here is a link to my master's publication discussing predictors of performance -

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If you have a question or topic you want us to address, leave a comment!

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Interested in testing, courses, or other long form content check out the critical oxygen website -


00:00 – Introduction

The hosts discuss the importance of oxygenation in working muscles and its role in performance characteristics like VO2 Max.

1:04 – Remote Physiology Assessment in Kona

The conversation shifts to plans for Kona's Iron Man World Championships, discussing physiological assessments and remote testing.

4:11 – Training Zone Adjustments

They delve into training zones, emphasizing the narrow transition points and the importance of adjusting zones based on fitness changes.

6:12 – Monitoring and Adapting Training Zones

Further discussion on the significance of testing post-rest season and adjusting training zones accordingly.

8:05 – Expanding Testing to Running and Rowing

Exploration of the expansion of testing methods to other activities beyond cycling and its potential benefits.

9:29 – Challenges in Implementing Treadmill Assessments

Challenges related to implementing treadmill assessments due to the difficulty in maintaining steady power or speed.

10:00 – Availability of Remote Testing

Details about the availability and affordability of remote testing through specific platforms and companies.

15:04 – Despair in Training vs. Ultra-Marathon

Reflections on the mental aspect of training versus participating in an ultra-marathon, highlighting the importance of control.

16:52 – Gut Training Experiment with Milk

A unique experiment involving consuming milk during exercise for specific gut adaptation purposes, despite potential challenges.

20:06 – Carbohydrate Intake and Fuel Oxidation

Comparative discussion on alternative carbohydrate intake methods during exercise, contrasting with the milk experiment.

22:11 – Discussing Training Intensity and Hydration Strategies

A conversation about training intensity and hydration methods, exploring factors like sweat loss, sodium intake, and using electrolyte supplements.

25:24 – Importance of Capillaries, Myoglobin, and Mitochondria

Focus on the significance of capillaries, myoglobin, and mitochondria in transporting and utilizing oxygen for endurance performance.

25:58 – Research on Traditional Predictors of Performance

Exploring a research paper comparing traditional predictors like VO2 max, threshold, and efficiency against a 40-kilometer time trial.

29:00 – V02 Max Test Methodology

Detailed discussion about V02 max testing methodology, including ramp tests, verification tests, and efficiency data collection.

32:02 – Near-Infrared Spectroscopy (NIRS) Calibration

Explaining the calibration process of NIRS devices for measuring tissue oxygenation and its importance in non-invasive muscle assessments.

33:02 – Arterial Occlusion and Cuffing Protocol

Describing the arterial occlusion and cuffing protocol used to gauge muscle oxygenation and its validation against in vitro methods.

39:14 – Personal Experiences as a Participant

Sharing personal experiences as a participant in studies, emphasizing the importance of researchers experiencing procedures firsthand.

43:05 – Regenerative Medicine and Mesenchymal Cell Injections

Discussing regenerative medicine techniques like mesenchymal cell injections and their potential role in injury recovery and sports performance.

44:35 - Introduction to Regenerative Medicine

Discusses the 50/50 success rate of a non-invasive injection treatment, weighing its value against invasive surgery.

48:16 - Personal Experience with Regenerative Medicine

Anecdotal experience with a shoulder injection, exploring the potential benefits and long-term effects of regenerative medicine.

49:32 - Discussion on 25-Kilometer Time Trial Protocol

Details the protocol for a cycling time trial used in a study, focusing on performance prediction and correlations.

50:10 - The Role of Oxygen in Muscles

Explores the significance of oxygen delivery, utilization, and the oxygenation balance in muscle during exercise and performance.

51:53 - Traditional Predictors of Performance

Discusses how traditional predictors, including V02 Max, were found to predict a significant portion of time trial performance.

53:04 - Near-Infrared Derived Predictors of Performance

Examines the high predictive capacity of near-infrared measurements (NIRS) compared to traditional predictors in performance analysis.

54:09 - Implications of the Study

Discusses the significance of biological variables in explaining traditional performance measures, showcasing their equivalence.

57:00 - Oxygen Delivery and Utilization

Highlights the crucial role of oxygen delivery and utilization in determining muscle oxygenation, fatigue, and overall performance.

1:00:03 - Shifting Oxygen Balance in Muscle

Discusses how exercise and training affect oxygen balance, emphasizing the importance of robust mitochondria for performance.

1:02:07 - Summary: Oxygenation in Working Muscle

Summarizes the critical role of balancing oxygen delivery and utilization in influencing key performance metrics like V02 Max and metabolic thresholds.

1:03:39 - The Role of Mitochondria in Complex Life

Explores the central role of mitochondria in complex life forms and how understanding mitochondrial health impacts performance analysis.

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