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Sep 29, 2015

My guests today are Dr. Sam Cheuvront and Dr. Robert Kenefick

  • Two of the world’s leading scientists in hydration and fluid homeostasis
  • Going in alphabetical order, 
    1. My first guest is Research Physiologist and Team Leader of the Thermal and Mountain Medicine Division at the US. Army Research Institute of Environmental Medicine (also known as USARIEM). His research includes the study of environmental and nutritional factors influencing human work performance. He is a leader in the fields of human fluid needs, dehydration assessment, heat stress mitigation, and exercise thermoregulation. He’s published over 100 -peer-reviewed papers and book chapters. Our first guest is Sam Cheuvront, PhD, RD
    2. My second guest is Principal Investigator in the Thermal and Mountain Medicine Division at USARIEM. He has published over 90 peer-reviewed manuscripts, book chapters AND reviews on fluid homeostasis and the physiological responses to environmental stress. He served as the president of the New England Chapter of the American College of Sports Medicine and received their Honor Award in 2012. He is also part of the Ultra Clan as an ultra marathon runner himself. Our second guest is Robert Kenefick, PhD.

My guests work for the U.S. Army. So, we must provide the disclaimer that "The views and/or opinions of Dr.'s Kenefick and Cheuvront are theirs personally and do not reflect the views or opinions of the U.S. Army or DoD."


This episode is the first in a two part series on fluids, hydration, and electrolyte physiology pertaining to ultra marathon running. We’re starting with the basics and progressing to specific application.

In this episode, you'll learn the answers to:

  1. What are the major body fluid and compartments and definitions the major relevant terms (de/eu/hyperhydration, hyper/hypovolemia)?
  2. What are the mechanisms/routes and quantities of water loss?
  3. How much water does a person need each day?
  4. Drinking to thirst - is it sufficient, like you hear commonly? (spoiler: NO!)
  5. How much salt is lost in sweat - only sodium? To what extent does this change throughout the time-course of an ultra marathon?
  6. What’s in sweat and what are ranges of rates and composition in running?
  7. During exercise, the majority of water gained is in the form of what we drink. But we have heard about getting water also from the breakdown of stored glycogen. Is this accurate?
  8. How can we expand our plasma volume?
  9. When do we need (and not need) an electrolyte-containing drink either during or after exercise?
  10. What is needed in an electrolyte drink beyond sodium?
  11. Hyponatremia; should it be a concern for most ultra marathon runners? 
  12. When does a runner need to consciously add sodium, beyond just following cravings?