The Tour De France is a unique test. Weeks long, extreme temperature variations, exhaustive exercise day after day, and otherworldly nutritional demands; Is there a better place to learn and maximize performance for the athlete?  One of the areas of deep interest over the last several years is the relationship of hydration, thermoregulation, and performance. This is especially important as we enter the summer here in Asia where temperatures soar . . .

Last week I went to a presentation by Dr. Stacy Sims, a post doctoral research fellow, and exercise physiologist at Stanford University. Dr. Sims was part of an exciting project with Dr. Allen Lim, x-chief physiologist for Garmin-Transitions. Their goal was to help the team optimally prepare for the Tour De France, and to create effective thermoregulation and hydration fueling strategies for the race.

Are you hydrating enough?

Their project focused on a few critical components, namely a pre-race preparation/acclimation phase, the daily nutrition and recovery of the athletes, and the pre, during, and post event hydration needs. Through the course of the presentation Dr. Sims touched on some rather interesting approaches and outcomes.

Hydration and Thermoregulation

First some background on water, hydration and thermoregulation. The human body is 55-65% water. Water is an essential aid in biochemical and metabolic reactions, it cools the body, and helps maintain the acid base balance.

Hydration is the equilibration of total body water (TBW) carried in the intracellular (66% of TBW) and extracellular (33% of TBW) spaces. Dehydration, medically speaking, is when the body contains insufficient water volume to maintain normal body function.

One of the foundational responsibilities of water is thermoregulation. Thermoregulation is “the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different.”  For you and I, that means maintaining homeostasis between 37 – 40C (72-100F). Thermoregulation is vital to the maintenance of exercise intensity. Find yourself much on either side of that range and you are in for some trouble.

The Problem(s)

Dehydration, and it’s role in thermoregulation and performance is broad and complex.

It has been shown that a state of dehydration of as little as one percent (1%) leads to decreased aerobic endurance. At three percent (3%) there is a decrease in muscular endurance, while at four percent (4%) there is decreased muscle strength, fine motor skill, and heat cramps. In addition the maintenance of blood volume is essential for maintaining stroke volume and plasma volume.

Don't take your water for granted!

Different athletes have different sweat rates, but most will sweat at between 1.5 – 3.0 Liters per hour. That means a 150 pound cyclist can reach 3% dehydration in as little as 45 – 60 minutes with no fluid intake (1 Liter = 1 Kilogram = 2.2 pounds). Unfortunately, gastric emptying is typically in the range of 0.8 – 1.3 Liters per hour, so you are on the defensive immediately. The more so if you start your race or training session hypo hydrated (0.5-1% dehydrated) as most of us do by some estimates. You simply can’t drink enough fluid to offset the loss from sweating.

All of this sweating leads to thirst. There are two kinds of thirst. Hypervolaemic thirst is the result of sweating, respiration, and/or bleeding. It is a decrease in the extracellular fluid and blood volume. Osmotic thirst is the result of a decrease in the intracellular fluid (e.g. too many solutes). Both depletions must be addressed prior to the onset of thirst.

While there are many products on the market that purport to help with your hydration and electrolyte balance, the truth is that most of them also contain a significant carbohydrate (CHO)  load in order to also be seen as a viable fuel source (yet not quite enough to actually be a viable fuel source) and to be palatable. There are a couple of downsides to this. First, the CHO actually serves to increase core temperature (gotta process that food!), secondly it impedes gastric emptying. Often these sports-drinks contain too little sodium to effectively replace sweat salt losses as well. Sodium loss through sweating ranges between 0.8 – 4.0g/hr

Keen to learn more about keeping your performance high and your body temperature low? Tune in next Thursday for Coach: Hydration Strategies for Summer Part 2: The Effects!

About Matt McNamara: Matt is a USA Cycling Level 1 coach with over 20 years of racing, coaching and team management experience. He is the founder and president of Sterling Sports Group, a performance coaching company focused on creating a seamless interface between athlete and coach, technology and personal attention. Learn more by visiting his website at www.sterlingwins.com.

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