Hydration 1 of 4: Endurance Events and the Magic of the Human Body

I have just finished reading a book of priceless scientific value authored by the most prominent expert in the field, Dr. Tim Noakes. The work titled “Waterlogged, The Serious Problem of Overhydration in Endurance Sports” is the must-buy of 2012. All health professionals (including nutritionists) who still make recommendations such as the following should read this book for their professional conscience: “it is essential to drink fluids if you want to keep the same weight during endurance events,” “you must drink before you get thirsty,” “losing over 2% of your body weight is detrimental to performance and your health,” “it is recommended to drink over 800 ml/hour,” “IV treatment is the best choice for marathon runners who are dizzy or who faint.”


In the wake of our past ticket titled “Drinking before getting thirsty?” (http://www.therunningclinic.ca/blog/2011/10/boire-avant-d’avoir-soif-drinking-before-getting-thirsty/), we have written a series of posts on hydration for marathon runners. This week, we present the first of four tickets:


  1. Endurance Events and the Magic of the Human Body;
  2. Dehydration, Performance, Cramps and Sodium;
  3. The Science of Hydration and its Consequences – Behind the Scenes;
  4. What’s Next?


For further enlightenment with regard to the fundamentals of this subject, you will find below quotes from Tim Noakes’s last book. It reads extremely well and features rigorously supported arguments that will put you off or even shock you at times. Humans developed as long distance runners especially well adapted to run in extreme dry heat in the middle of the day while drinking infrequently (p.35)


  • Bipedalism , little body hair, unequalled sweating capacity, and the ability to resist the effects of thirst and water loss make human the premier hot weather runner. (p.14)
  • Biped has 60% less surface area exposed to the sun than does a quadruped of the same mass. (p.15)
  • Sweating provides humans with the largest radiator of any mammal. Panting (what’s do the majority of other mammals) does not produce anything like the same cooling capacity. (p.22)
  • Human can safely exercise for 8-10hours in the heat while requiring little fluid replacement (p.19)
  • Exhaustion occurred before the rectal temperature reaches dangerous levels… because the concept of “anticipatory regulation” to protect body temperature homeostasis (p.47)
  • The brain modifies the exercise behaviour “in anticipation” by causing the athlete to exercise more slowly in hot environmental condition (p.77)
  • The higher rectal temperatures in athlete are measured on short and intense activities (p.72)
  • Athletes in competitions frequently raise their body temperatures above 41 degrees Celsius without showing any evidence of heat illness (p.207)
  • Since the sweat rate is not reduce in athletes who become dehydrated during exercise, dehydration does not impair the capacity of dehydrated athletes to lose heat during exercise. (p.222)
  • Dehydrated athlete could sweat more (to lose more heat) OR choose to exercise at a higher, but regulated, temperature (water-conserving mechanism). (p.222)
  • More sever level of weight loss or dehydration are not related to body temperatures
  • Less gifted runners have a lesser risk of heat illness because they run slower at a lower metabolic rate, and thus usually at lower body temperature. (p.226)


Sweating during exercise cause water loss, which stimulates thirst. When fluid is available humans can drink enough to satisfy their thirst.


  • There is no immediate health risk associated with the level of dehydration of 7-10% present at the termination of exercise (p.48)
  • Thirst is the symptom that is felt with the greatest intensity at all levels of weight loss (p.51)
  • The only symptom of dehydration is thirst, which become increasingly persistent and impossible to ignore as the level of fluid persist (p.147)
  • Human do not regulate body weight during exercise; rather they regulate the osmolality of the body tissues and most especially that of their most important organ, the brain. (p.258)


In conclusion: Runners should aim to drink ad libitum (according to thirst) 400-800ml/hr (13.5-27 fl oz/hr) with the higher rates for faster, heavier runners competing in warm environmental conditions. (p.334) Next week: “Dehydration, Performance, Cramps and Sodium”