The Largely Baffling and Conflicting Theories of Race Hydration (and my 3 little steps to keep it simple)

If you haven’t had the pleasure of enduring a death march at the end of your triathlon due to dehydration then pat yourself on the back!  Top performance relies on proper hydration, particularly in long course events.  Given its importance, you’d think that the guidelines would be pretty straight-forward.  Well, not so fast my friend.

There are two polar opposite theories for ideal endurance racing hydration:  That of the American College of Sports Medicine (ACSM) and the other by those who are proponents of what I call the ‘Drink to Thirst’ Theory.

But before we get too deep into the details, I’d like to give you some basic definitions for reference:

1. Euhydration: A balanced state in which the amount of body water meets the body’s physiological demands.
2. Dehydration: It’s the loss of body water.   The American College of Sports Medicine (ACSM) is considered the authority in the U.S. and in the ACSM’s 2007 position paper on Exercise and Fluid Replacement it set dehydration of 2% as the point where aerobic exercise performance begins to degrade.
3. Osmolality: It is the concentration of body fluids.  For the purpose of this article we’ll use it to refer to the sodium concentration, which ranges from 130mM-155mM (mille mole)/liter of body fluid with 140mM/liter most often used as normal.
4. Sweat rate: It’s the rate at which you lose fluid and minerals, primarily sodium chloride (salt), during exercise.  Sweat rates vary greatly as does the concentration of salt within the sweat.  Depending on which source you refer to the salt concentration in sweat is anywhere from 10mM-80mM/liter.
5. Hyponatremia: An over consumption of fluid resulting in a low concentration of sodium in the blood…125mM-130mM/liter or lower.
6. Metabolic rate: This refers to your work rate and is the key determinant of your core body temperature…the faster you go the more heat you generate.
7. Anti-diuretic hormone (ADH): ADH is released with small changes in the body’s osmolality.  The release of ADH prevents your body from losing more water through urination.

The Two Theories

Remember, these are only theories and both camps are passionate about their respective position.

The ACSM provides general guidelines for pre-exercise, during exercise, and post-exercise hydration designed to cover all sports not just endurance sports.  The opposing theory, what I’ll call the ‘Drink to Thirst’ theory, really focuses on hydration during endurance exercise and in particular during long distance running races with more and more emphasis on long course triathlons.

Theory #1: The ACSM Position:  Thirst is not enough

In 2007 the ACSM released its position paper on Exercise and Fluid Replacement which essentially changed some their previously stated positions.  The changes appear to be primarily driven by the research of Tim Noakes and his followers.  The most notable changes were:

• the drink as much as tolerable position was removed, and;
• the acknowledgement that Body Weight (BW) losses up to 2% had no detrimental effect on aerobic exercise performance.

Pre-Race:  The ACSM provides specific hydration guidelines to ensure you begin your exercise/race in a euhydrated state.

• Drink 5-7mL/Kg of body weight 4 hours before the race.
• Drink another 3-5mL/Kg of body weight 2 hours before the race.

Again these are general guidelines designed to cover a variety of sports, particularly weight class sports where dehydration prior to an event may be an issue.  When it comes to endurance racing, my experience based on the length of the port-a-potty lines on race morning is that starting the race fully hydrated is not much of an issue for athletes.

During Race Hydration:  The ACSM is very specific in that they believe that thirst alone is not a good indicator of when to drink, particularly for older athletes.  In addition two key changes are drinking to equal your sweat rate instead of as much as you can tolerate and the acknowledgement that a loss of up to 2% of body weight (BW) due to dehydration has no effect on aerobic exercise performance.  They also encourage the consumption of electrolytes, particularly sodium and potassium.  The primary purpose of the electrolytes is to stimulate thirst and retain fluid while replacing some of the electrolytes lost in sweat.  The specific guidelines are the following:

1. Consume 3-8oz fluid/15 minutes for activities lasting longer than 60-90 minutes.
2. Consume 500-700mg sodium/liter/hour.

Post-Race:  the post –race recommendations are to rehydrate to compensate for BW losses.  The specific recommendations are:

1. Consume 150% of the weight lost over a 6 hour period…24oz fluid for every pound lost.
2. Consume salty food or a sport’s drink containing electrolytes to replace electrolytes lost.

Theory #2:  Drink to Thirst

Supporters of this theory believe the body’s thirst mechanism is highly developed and that only water should be consumed during training and racing.  Of much less importance is the level or percentage of dehydration, particularly since there’s such large variation in the ability of individuals to tolerate different levels of dehydration.  The key components of this theory are the following:

1. Your body is more concerned with the concentration of body fluids as opposed to weight.
   • The electrolyte concentration in the body is significantly higher than the electrolyte concentration of even a “salty sweater” (not something you wear in chilly weather, mind you, but sweater meaning a person who sweats).
   • Since fluid loss from sweat is greater than electrolyte loss, the electrolyte concentration in the body increases as you sweat, your body’s thirst mechanism kicks-in to rebalance your body’s fluid concentration, and you consume water to satisfy the thirst, which rebalances the body’s fluid concentration.
2. There’s no need for electrolyte consumption if you drink to thirst.  Since the concentration in your body fluids is high there’s no advantage to consuming additional electrolytes.  The disadvantage is that you’ll over-consume fluids, which will drive your concentration low…in the extreme the result would be hyponatremia.
3. Don’t try to drink to match your sweat rate.  Focus on drinking to thirst, which for most athletes will be between 30-50% of sweat rate.

Here are some other things you need to add into the equation:

Athlete Specific

1. Your size:  Larger athletes have greater surface area that requires cooling, which is why women generally have lower sweat rates.
2. Your weight:  The key consideration in body weight relative to hydration is total body water (TBW).  Fat-free mass, which is 70%-80% water, is the key determinate of TBW.  60% TBW is commonly used for trained athletes…the percentage is a little lower for women due to higher levels of adipose (fat) tissue even in trained female athletes.
3. Your training level:  The better trained you are the more efficiently your body can function in training and racing.
4. Your metabolic rate:  This refers to work rate and is the key determinant in how fast you’ll dehydrate.  The higher your work rate the more heat you produce.  In order to dissipate this heat and cool the body your sweat rate has to increase.
5. Your duds:  What you wear matters.  Heavier, non-breathable fabric traps the heat and increases the sweat rate for a given work rate.
6. Your genes:  Each of us has unique genetic characteristics that determine our sweat rate that are independent of age, training level, etc.
7. Acclimatization:  The better acclimated you are to the environmental conditions of the race venue the more effectively your body can manage it.  The amount of time required to acclimate varies by individual but 2 weeks is the time frame most often cited as adequate.

External Factors

1. Heat:  The higher the temperature the higher the sweat rate required to maintain a given work rate.
2. Humidity:  In humid conditions your sweat is unable to evaporate trapping the body heat your sweat’s trying to dissipate.
3. Altitude:  At altitudes above 2300 feet it’s common for athletes to have greater fluid losses than at sea level for the same exercise.

So now that you are bursting with all this data, you’re probably saying, “So what should I do?
I still need a plan!”

Well, don’t sweat it.  Developing your hydration strategy doesn’t have to be an overly complicated process.  Actually the simpler the plan the easier it will be to follow.  As for which hydration theory you should follow… Well that’s up to you.  Personally I believe both have strengths and weaknesses so I tend to blend the theories.  Specifically, I do the following:

1. Bike hydration:  I target consuming fluid equal to 60-80% of my sweat rate on the bike.  This allows the ADH to kick in to minimize the need to urinate and lets me start the start the run reasonably hydrated.  Besides it’s much easier to hydrate on the bike.
2. Run hydration:  My run hydration goal is approximately 30-50% of sweat rate.  This is just an estimate as it’s particularly hard to measure actual hydration when running through an aid station.
3. Sodium:   I do consume sodium both during the bike and run legs of the race.  The sodium offsets some of what’s lost in sweat and allows me to consume a bit more fluid than I might otherwise.  It works for me.

Here are my 3 key steps to figuring out how to properly hydrate for long-course triathlon:

1. Weigh yourself:  At least once a week weigh yourself before and after a training session.  Keep a log handy to track the changes in weight.  I like one hour runs or bike trainer sessions because I don’t need to drink making it easy to determine sweat rate from changes in weight.  Also track the air temperature if possible in your log to get an idea of how it affects your sweat rate.  For calculation purposes 1 pound = 16 fluid ounces or .95 kilograms = 1 liter. This isn’t perfect science but it’s simple and pretty effective.
2. Be flexible:  There is no one perfect hydration plan that works for all situations.  Do your homework on your hydration needs and adjust to the conditions on race day.  If it’s warmer or cooler than expected hydration needs to be adjusted up or down, respectively to match your race pace to the conditions.
3. Keep your head in the race:  Your thirst mechanism was developed over thousands of years of evolution but your race emotions weren’t.  Learning to stay calm and focused puts you in control of the number one rule of long course triathlon racing, which is take care of yourself at all times in the race.

Until next time train safe, stay healthy, and hope to see you at the races.