Jan 5, 2016
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
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
You can connect with Dr. Joyner at:
Dr. Joyner answers many questions, including:
- What are the definition(s) of fatigue?
- How does ‘fatigue’ differ from ‘tired’ and where do they
- 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
- 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
- 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?
- What is the physiological basis of cardiac drift and does it
have a role in fatigue or exhaustion?
- 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?
- What do we know about aging an endurance performance relevant
- 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?
- What do we know about the nature of systemic feedback signals
to the brain that may contribute to fatigue/exhaustion in
- 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?
- What role does sleep deprivation play in
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.
- What are the most common misunderstandings for misconceptions
about fatigue and exhaustion in ultra endurance performance?
- 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)?