Critical Oxygen

In this episode, Dr. Billy Sperlich and I discuss training intensity distributions and the use of wearables in endurance sports. He shares his background in exercise physiology and his interest in triathlon. Dr. Sperlich explains the challenges of defining training intensity distribution and the limitations of research in this area. He highlights the importance of individualization and regularly testing and adjusting training intensity zones. We define pyramidal training intensity distribution and the misconceptions and practical implications of polarized training. Paper: The proportional distribution of training by elite endurance athletes at different intensities during different phases of the season - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10641476/ TAKEAWAYS 1) Choose a quantification method for training intensity and stick with it for consistent results. 2) Consider the impact of culture and mentality on sports performance, as different countries have different sporting traditions and values. 3) Use wearables to monitor training, but be aware of the limitations and choose the right technology for your training model. 4) Identify key elements in your training model and evaluate their effectiveness to make informed adjustments.Enjoying these podcasts, subscribe to get notified when new episodes are released. If you have a question or topic you want me to address, leave a comment!Follow me on Instagram - https://www.instagram.com/criticalo2 Follow Dr. Sperlich on instagram - https://www.instagram.com/billysperlich/?hl=enCheck out his latest research - https://www.researchgate.net/profile/Billy-Sperlich OUTLINE: 00:00 Introduction 01:28 Guest Introduction 02:25 Dr. Sperlich's Background and Interest in Exercise Physiology 03:25 Transition to Triathlon 04:43 Interest in Combining Different Disciplines 06:08 Interest in Nutrition and Heat Regulation 07:34 Involvement in High Altitude and Other Specialized Fields 08:32 German Training Science Tradition and High Volume Training 09:02 Early Interest in High Intensity Interval Training 10:30 Challenges and Misconceptions of High Intensity Interval Training 11:21 Research on High Intensity Interval Training in Children 12:16 Shift in Training Philosophy and Polarized Training 13:13 Calibrating Training Intensity Distribution 14:27 Comparison of Training Intensity Distributions 15:49 Definition of Training Intensity Zones 16:49 Different Intensity Clustering in Different Sports 18:12 Challenges in Defining Training Intensity Zones 19:42 Quantifying Training Intensity Distribution 20:39 Training Intensity Distribution in Endurance Sports 21:34 Differences in Training Volume in Different Sports 22:30 Challenges in Comparing Different Types of Exercises 23:23 Quantification Methods for Training Intensity 27:07 Impact of Culture and Mentality on Training Intensity 31:48 Importance of Training History in Defining Training Intensity 33:14 Training Intensity Distribution in Cross-Country Skiing 34:08 Variation in Training Intensity Distribution 35:29 Importance of Zone 1 Training for Runners 39:14 Polarized Training in Cross-Country Skiers 41:30 Shift in Training Intensity Distribution during Competition Phase 43:52 Limitations of Single Case Studies and Cross-Country Skiing Bias 46:14 Variability in Training Intensity Distribution 50:32 Importance of Considering Sport-Specific Training Intensity Distribution 53:00 Impact of Culture and Mentality on Training Intensity 59:05 Differences in the Repeat VO2 Max Study 59:33 Using Wearables to Inform Training 01:00:31 Choosing a Training Model 01:01:55 Types of Wearables for Training 01:03:23 The 24-Hour Thinking Approach 01:04:48 Measuring Sleep Quality with Wearables 01:05:44 Identifying Technology for Training 01:07:10 Key Elements for Successful Training 01:08:39 Considering Biological and Measurement Variability 01:09:38 Where to Find Dr. Sperlich

In this episode of the Critical Oxygen podcast, Aaron Geiser and I discuss VO2max protocols and how to make aerobic development fun. We address misconceptions about VO2 max and the importance of individualized training. We also explore different breathing techniques that may be able to improve performance and discuss the various VO2max protocols available. In this episode, we discuss various aspects of VO2max training. We emphasize the importance of considering research and the specific needs of individual athletes when designing training programs. We also discuss adjusting output levels based on interval duration and the importance of recovery. The conversation touches on block periodization and making intelligent training decisions. The episode concludes with a teaser for the next episode, which will focus on making aerobic development more enjoyable. TAKEAWAYS 1) Consider the research and the specific needs of individual athletes when designing VO2max training programs. 2) Adjust output levels based on the duration of intervals to ensure appropriate intensity. 3) Recovery is crucial for high-intensity training, and easy aerobic workouts can aid in the recovery process. 4) Make intelligent training decisions based on your own fitness level and goals, rather than blindly following popular training methods. 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 Follow Aaron on Instagram - https://www.instagram.com/triageiser/ CHAPTERS 00:00 Introduction and Misconceptions about VO2 Max 19:58 Breathing Techniques for Improved Performance 22:20 Different VO2 Max Protocols 32:43 Individualized Approach to VO2 Max Training 45:15 Considerations for VO2 Max Training 51:04 Improving Oxygen Uptake and Research Considerations 53:25 Adjusting Output Levels for Different Interval Durations 55:22 Tailoring Training to Individual Needs 57:42 Maintaining Mental and Physical Energy 59:09 Importance of Recovery and Contextual Training 01:00:39 Considerations for Block Periodization 01:01:36 Making Intelligent Training Decisions 01:02:32 Context and Content in Training 01:03:00 Teaser for Next Week: Making Aerobic Development Fun

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

In this episode of the Critical Oxygen podcast, Aaron Geiser and I answer listener questions about endurance development, periodization, and training in a fasted state. We discuss the importance of balancing volume and intensity in training, and how to structure a long training cycle. We also explore the use of heart rate and watts for training, and the benefits and considerations of training in a fasted state for fat burning. Overall, the conversation emphasizes the importance of individual context and goals in designing an effective training program. The conversation covers topics related to fueling before, during, and after workouts, the importance of calorie deficit/maintenance, body weight and body fat percentage, the diversity of body types in triathlon, factors to consider for ideal race weight, assessing wellness and performance, weight as a factor in long course triathlon, and the Zwift long ride as a community platform. TAKEAWAYS 1) Proper fueling before, during, and after workouts is crucial for performance and recovery. 2) Being in a calorie deficit for extended periods can lead to self-cannibalization and hinder performance. 3) Body weight and body fat percentage should be considered in the context of overall health and performance. 4) Triathlon is a sport that embraces diversity of body types, and success is not limited to a specific ideal body weight or body fat percentage. 5 )Assessing wellness and performance through factors like mood, recovery, and nutrition is more important than focusing solely on weight. Enjoying these podcasts, 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 Follow Aaron on Instagram - https://www.instagram.com/triageiser/ CHAPTERS 00:00 Introduction and Listener Questions 02:18 The Importance of Volume and Intensity for Endurance Development 06:11 Periodizing a Long Training Cycle 13:41 Using Heart Rate and Wattage for Training 17:28 Periodizing a 12-Month Training Cycle 21:35 The Specific Phase of Training 23:56 Tapering and Competition Phase 30:13 Training in a Fasted State and Fat Burning 52:33 Fueling before, during, and after workouts 55:37 The importance of calorie deficit 56:34 Body weight and body fat percentage 59:31 Diversity of body types in triathlon 01:00:54 Factors to consider for ideal race weight 01:04:30 Assessing wellness and performance 01:07:58 Weight as a factor in long course triathlon 01:09:17 Zwift long ride as a community platform

In this episode, I talk with Coach Sean Seale from Upside Strength. He discusses his background in coaching and how his approach has evolved over the years. We emphasize the importance of bridging the gap between science and training, and the need for coaches to understand the individual needs and preferences of their athletes. We also highlight the benefits of cycling as a training modality and the importance of considering the demands of training in addition to the demands of the sport. We conclude by discussing the importance of balancing intensity and volume in training programs. This conversation explores the importance of balancing fatigue and recovery in training. It emphasizes the need to find the right balance between accumulating fatigue and allowing for adequate recovery. The discussion also delves into the concept of zone 2 training and its benefits for performance improvement. It highlights the significance of identifying zone 2 boundaries and provides practical methods for implementing zone 2 training into a training plan. Overall, the conversation emphasizes the importance of incorporating lower intensity training and daily physical activity for optimal performance and overall health. TAKEAWAY 1) Understanding the individual needs and preferences of athletes is crucial for effective coaching. 2) Cycling is an underutilized training modality that can yield great benefits for athletes in various sports. 3) Training programs should consider the demands of training in addition to the demands of the sport. 4) Balancing intensity and volume is key to optimizing performance and preventing overtraining. 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 Follow Sean on Instagram - https://www.instagram.com/upside_strength/ OR Youtube -  @Upsidestrength  Interested in testing, courses, or other long form content check out the critical oxygen website - https://www.criticaloxygen.com CHAPTERS 00:00 Introduction and Background 01:30 Getting into Coaching 03:00 Bridging the Gap Between Science and Training 08:00 Coaching Approach and Collaboration 10:40 Evolution of Coaching Approach 17:00 Introduction to CrossFit 21:30 Assessments and Testing 25:00 Benefits of Cycling 32:00 Importance of Training Demands 38:30 Balancing Intensity and Volume 39:21 Balancing Fatigue and Recovery 48:43 Identifying Zone 2 Boundaries 57:23 The Importance of Zone 2 Training 01:01:13 The Benefits of Going Easier

In this episode of the Critical Oxygen podcast, Dr. Robert Jacobs and I discuss exercise economy and efficiency. We explain the importance of zone two training for improving volume and intensity, and it's role in increasing economy. We define exercise economy as the amount of oxygen per wattage or unit speed and discuss its measurement challenges. We also explore the factors that affect economy and efficiency, such as aging, experience, and biological changes. Additionally, we highlight the benefits of lifting heavy weights and provide practical examples for improving efficiency through strength training. TAKEWAYS 1) Increasing volume by completing zone 2 training can help to improve running economy. 2) Heavy strength, powerful lifting, and plyometrics can help to improve economy and efficiency. Good papers Systematic review comparing plyometrics and heavy strength work: https://pubmed.ncbi.nlm.nih.gov/36370207/ Optimizing strength training for running and cycling endurance performance: https://pubmed.ncbi.nlm.nih.gov/23914932/ 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/criticalo2Interested in testing, courses, or other long form content check out the critical oxygen website - https://www.criticaloxygen.com CHAPTERS 00:00 Introduction and Zone Two Training 19:02 Definition and Importance of Exercise Economy and Efficiency 27:41 Factors Affecting Economy and Efficiency 36:11 Lifting Heavy Weights for Improving Efficiency 48:34 Practical Examples for Improving Efficiency 52:28 The Importance of Rest and Heavy Strength Training 55:12 Kettlebell Workouts and Applied Resistance Training 57:00 Flexibility Training and its Impact on Efficiency 59:16 Closing Remarks

In this episode of the Critical Oxygen podcast, I am joined by coach Michelle Simmons to discuss the intersection of science in coaching! We cover topics such as understanding thresholds and energy systems, the evolution of training and coaching, the role of lactate in training, fueling for performance, the myth of fasted training, carbohydrate and fat oxidation, the importance of being a hybrid athlete, and the role of mitochondria in energy production. The discussion covers fatigue resistance and the role of mitochondrial function in staving off fatigue. We explore the benefits of easy training and high-intensity interval training. The conversation touches on lactate production and consumption, as well as the use of lactate as a fuel source. The importance of carbohydrate intake and its impact on performance is discussed, along with the need for individualization in training and nutrition. More about Michelle in her words: Personally: I did my first triathlon in 1995! Fell in love with it immediately. I continued to race for ~25 years. I rarely race anymore but I still train bc I enjoy it and want to be healthy and fit enough to train with my athletes at times. In my time, I did 18x Ironmans, including 4x in Kona. Professionally: I started coaching a few friends in 2008. I took every opportunity to learn (still do!) and my coaching business grew to the point where I’ve been doing it full time for the last 15 years. I am the founder and Head Coach at TeamBSC Triathlon. I work with amateurs of all ages and abilities- some beginners and others who ultimately qualify for the World Champs! I’m actively involved in supporting endurance sports on Oahu. I coach Kailua Masters Swim team, lead a local monthly Girls Ride, and am a board member for Aloha State Bike Racing Association. Sometimes I present educational workshops for local athletes. TAEKAWAYS 1) Understanding thresholds and energy systems is crucial for optimizing training and performance. 2) Coaching and training have evolved over the years, with a greater emphasis on individualization and understanding the underlying physiology. 3) Fueling properly before, during, and after workouts is essential for performance and recovery. 3) Mitochondria play a key role in energy production. Mitochondrial function plays a crucial role in fatigue resistance. 4) Easy training and high-intensity interval training both offer unique benefits for endurance athletes. 5) Lactate production and consumption are complex processes that contribute to energy production. 6) Carbohydrate intake should be individualized based on an athlete's specific needs and goals. Enjoying these podcasts, 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 Follow Michelle on Instagram - https://www.instagram.com/mama_simmons_/ Or visit her website - https://www.michellesimmonscoaching.com/ CHAPTERS 00:00 Introduction and Background 03:00 Learning from Experience and Coaching 08:00 Understanding Thresholds and Energy Systems 13:00 The Evolution of Training and Coaching 19:00 The Role of Lactate in Training 25:00 Fueling for Performance 32:00 The Myth of Fasted Training 38:00 Carbohydrate and Fat Oxidation 45:00 The Importance of Being a Hybrid Athlete 46:00 The Role of Mitochondria in Energy Production 47:01 Fatigue Resistance and Mitochondrial Function 49:00 Benefits of Easy Training and High-Intensity Interval Training 51:52 Lactate Production and Consumption 53:13 Cytomax and Lactate as a Fuel Source 55:44 Carbohydrate Intake and Performance 57:09 Debating Carbohydrate Intake 59:29 The Importance of Individualization 01:04:27 Simplifying Training and Nutrition 01:06:17 Practicality and Optimal Performance 01:09:29 The Role of Happiness in Performance 01:12:45 The Secret to Longevity in the Sport

Welcome to the Critical Oxygen Podcast! In this episode Dr. Robert Jacobs and I talk about falling in love with exercise training and how it's helped us become better at what we do! 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 OUTLINE: 0:00 – Introduction 1:13 – The benefits of being an entrepreneurial PhD 2:07 – Plans for setting up a home physiology testing facility 3:00 – The advantages of an entrepreneurial lifestyle 4:00 – Competitive spirit in bike training 5:43 – Personal cycling achievements and challenges 8:01 – The significance of graded exercise protocols 9:04 – Discussion on optimizing performance 11:09 – Thoughts on altitude training 15:06 – On optimizing performance 17:11 – Scientific communication is key! 17:54 – Differences between males and females in cycling 20:16 – The dangers of professional cycling 22:00 – The risks of outdoor road cycling 23:03 – The benefits of indoor cycling 24:00 - Concerns about running outdoors 24:36 - Encounters with unruly drivers 25:11 - Maximizing performance and embracing discomfort 27:05 - World record in female marathon 28:44 - Reflecting on personal progress 31:51 - Importance of work-life balance 35:20 - Falling in love with exercise 38:35 - Balancing multiple responsibilities 46:13 - Morning Routine 47:10 - Nutrition on the Bike 47:23 - The Role of Nutrition 48:11 - Maurten Drink Mix 49:03 - Workout Performance 50:11 - Carbohydrate Composition 53:00 - Post-Workout Nutrition 58:21 - The Role of Exercise in Research 1:00:07 - Landscaping and Physical Work 1:01:27 - Conclusion

Welcome to the Critical Oxygen Podcast! In this episode Dr. Robert Jacobs and I talk about the importance of skeletal muscle in predicting endurance performance. We focus on the significance of capillaries, myoglobin, and mitochondria in endurance performance, along with research comparing predictors of performance. Here is a link to my master's publication discussing predictors of performance - https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.14342 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.ctiricaloxygen.com OUTLINE: 0:00 – Introduction 1:04 – Remote Physiology Assessment in Kona 6:12 – Training Zone Adjustments 7:01 – Monitoring and Adapting Training Zones 8:05 – Expanding Testing to Running and Rowing 9:29 – Challenges in Implementing Treadmill Assessments 10:00 – Availability of Remote Testing 11:35 – Ultra Marathon Nutrition Strategy 15:04 – Despair in Training vs. Ultra Marathon 16:52 – Gut Training Experiment with Milk 20:05 – Carbohydrate Intake and Fuel Oxidation 24:59 – Shifting Focus Back to Predictors of Performance 25:24 - Importance of Capillaries, Myoglobin, and Mitochondria 25:58 - Mitochondrial Function as a Key Predictor of Performance 26:15 - The Skeletal Muscle and Capillary Myoglobin Mitochondria Axis 26:33 - Research on Traditional Predictors of Performance 27:11 - Comparison to a 40-Kilometer Time Trial 28:13 - Diverse Study Participants 29:00 - V02 Max Test Methodology 30:24 - V02 Max Verification at 110% 32:02 - Near-Infrared Spectroscopy (NIRS) Calibration 33:02 - Arterial Occlusion and Cuffing Protocol 36:01 - Validation of Cuffing Protocol 39:11 - Personal Experiences as a Participant 43:05 - Regenerative Medicine and Mesenchymal Cell Injections 48:16 - The Benefits of Regenerative Medicine? 49:01 - Back to the Predictors of Performance 49:32 - The 25-Kilometer Time Trial 50:25 - The Role of Oxygen in Muscles 51:53 - Traditional Predictors of Performance 53:04 - Near-Infrared Derived Predictors of Performance 54:09 - The Implications of the Study 57:00 - Oxygen Delivery and Utilization 58:02 - The Significance of NIRS Measurements 1:00:03 - Shifting Oxygen Balance in Muscle 1:00:28 - The Importance of Robust Mitochondria 1:02:07 - Summary: Oxygenation in Working Muscle 1:03:36 - The Role of Mitochondria in Complex Life

This episode of the Critical Oxygen podcast discusses VO2max, the maximum amount of oxygen a person can uptake and utilize during exercise. Dr. Robert Jacobs and I provide a definition and historical context of VO2max, explaining its importance in determining aerobic potential. We then discuss the Fick equation and indirect calorimetry as methods to measure VO2max. The reliability and limitations of VO2max testing are explored, along with considerations for testing protocols. We also discuss training protocols to improve VO2max and highlight the importance of individualized approaches. Overall, the episode provides valuable insights into understanding and optimizing VO2max. TAKEAWAYS 1) VO2max is the maximum amount of oxygen a person can uptake and utilize during exercise, and it is an important indicator of aerobic potential. 2) The Fick equation and indirect calorimetry are used to measure VO2max, with cardiac output and VO2 difference being key factors. 3) VO2max testing has limitations and requires careful consideration of testing protocols and the expertise of the tester. 4) Training protocols to improve VO2 max include high-intensity intervals at or near VO2 max. 5) Individualized approaches to VO2max testing and training are important for optimal results. 6) The pulmonary system, including CO2 exchange, can be a limiting factor for VO2 max. 7) Exercise-induced arterial hypoxemia can impact VO2 max, particularly at high altitudes. 8) Cardiac output and stroke volume play a role in determining VO2 max. 9) Skeletal muscle mitochondrial adaptations can also influence VO2 max. 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 OUTLINE 00:00 Introduction and Background 01:24 Definition and Historical Context of VO2Max 04:12 Determining VO2Max: Fick Equation and Measurement Techniques 06:09 Indirect Calorimetry and Indirect Measurement of Energy Expenditure 08:08 VO2 Max Testing: Reliability and Limitations 18:07 VO2 Max Testing Protocols and Considerations 36:40 Improving VO2 Max: Training Protocols 45:48 VO2 Max Research and Practical Application 47:15 Introduction to the paper on VO2 max 48:12 Discussion on the pulmonary system 49:45 Consideration of gender differences 50:13 Limitations of male-biased research 51:32 Exercise-induced arterial hypoxemia 55:08 Importance of pulmonary system for CO2 56:22 Respiratory muscle training 57:45 Cardiac output and stroke volume 01:01:29 Importance of hemoglobin and cardiac output 01:05:07 Skeletal muscle mitochondrial adaptations 01:09:05 Importance of measuring VO2 max 01:09:46 Consideration of skeletal muscle as a limiter of VO2 max