My guest today is Michael Joyner, MD. He would need no introduction in the field of exercise physiology. Dr. Joyner is an integrative physiologist, scientist, and evidence-based Anesthesiologist at the Mayo Clinic. His specific areas of expertise include autonomic control of circulation, muscle and skin blood flow, exercise, oxygen transport and metabolic regulation in humans. Additionally, much of his lab’s work in these areas includes the study of aging. This work has been continuously funded by the NIH since the early 1990s. The list of his awards and honors is lengthy; suffice it to say that he has received many of the highest awards in the fields of physiology, medicine, and exercise. Most scientists would feel they had a worthy career with 2 or 3 seminal papers on a subject. My guest today has a list of seminal publications longer than many scientists complete lists. Dr. Joyner published over 350 scientific papers, and many books and book chapters; with many thousands of citations. Simply put, Dr. Joyner is one of the most influential figures in modern exercise science, from molecules & mechanisms to health advocacy. He is also an avid runner.   Later in the interview, you get a glimpse into his knowledge base in the history of running and runners. He rattles off runners and other elite athletes, their ages, and times of performance over many decades. This breadth and depth of knowledge allows him to bring to you amazing insights and many thoughtful ideas….including a haiku!   You can connect with Dr. Joyner at: His website on Human Limits of Performance Twitter: @DrMJoyner His clinical profile at the Mayo Clinic   Dr. Joyner answers many questions, including:  

1. What are the definition(s) of fatigue?
2. How does ‘fatigue’ differ from ‘tired’ and where do they overlap physiologically.
3. What are the causes of fatigue in extreme cases or high intensity: occlusion of blood flow, max sprint, constant effort at ~maximal lactate steady state (fatigue in about an hour or two)?
4. When we talk about VO2max, we generally consider the cardiovascular system - delivery of oxygen-rich blood - as the major limiting factor based on the knowledge that isolated muscle (like in single leg lifts) can consume more oxygen per 100 grams than that same tissue does at whole body VO2max. Is there a role of the cardiovascular system in exhaustion if we maintain fluid and electrolyte homeostasis?
5. Muscle micro-trauma is likely to be a major cause of fatigue in ultras. First, what exactly is the muscle trauma and damage that is occurring during ultra marathons? Second, is this likely to be a major source of fatigue?
6. What is the physiological basis of cardiac drift and does it have a role in fatigue or exhaustion?
7. Fatigue is very complicated when we consider running ultra marathons. What can we say are likely contributors? Are there any factors that might be contributors in higher intensity effort that are not likely to contribute to fatigue in an ultra marathon?
8. What do we know about aging an endurance performance relevant to fatigue?
9. In longer events, we are likely to become relatively depleted of stored glycogen before the end of the race. If our event lasts hours…perhaps many hours…longer, and we can consume and absorb 60-90 g of carbohydrates per hour - will substrate availability contribute to fatigue even if we slow down enough to match energy intake with utilization? In other words, is there anything about being in the depleted state for a long period of time (muscle cells contracting with little internal carbohydrate) that shifts efficiency so as to contribute to fatigue?
10. What do we know about the nature of systemic feedback signals to the brain that may contribute to fatigue/exhaustion in ultras?
11. What do we know about the brain and motivational fatigue in events that require moderate effort for many hours, over night, and some times even multi-day?
12. What role does sleep deprivation play in fatigue/exhaustion?

  We develop a list of the expected common or primary predicted sources of fatigue/exhaustion in ultra events.   We wrap up with two action questions.

1. What are the most common misunderstandings for misconceptions about fatigue and exhaustion in ultra endurance performance?
2. What are the 3-4 most important actions we can take to stave off fatigue or exhaustion in an ultra endurance event (what can we do about the most common causes)?