August 22, 2013

Do You Have A Drinking Problem?

Dehydration can turn a great day into a grueling death march in a very short order. Given the importance of hydration to performance, especially long course racing, you’d think that the guidelines for endurance race hydration would be straightforward. But that’s just not the case.

Currently there are two distinct and competing theories to hydration during endurance training and racing.

American College of Sports Medicine (ACSM) Position: Thirst Is Not Enough

This approach simple states that if you wait until you’re thirsty then it’s too late:  you’re already dehydrated so you might as well pack it up and call it a day.

Your goal then is to drink ahead of thirst. The ASCM originally detailed their hydration guidelines in their 1996 position paper on Exercise and Fluid Replacement. This position paper established specific guidelines for pre, post, and during exercise hydration that included all sports… not just endurance sports. In 2007 the ACSM revised/updated their position. The 2007 version made two key changes relative to the 1996 paper.

  • The drink as much is tolerable position was removed from this paper.
  • The new position paper acknowledges that body weight losses of up 2% have no detrimental effect on aerobic exercise performance.

The 2007 update also removed specific guidelines to drink within a specific range (a set amount of fluid every 15 minutes) to one based on body weight.  A reasonable change considering it’s unlikely that a 110 (50kg) pound woman needs as much fluid as a 220 pound (100kg) man.

Prerace Hydration Guidelines

The ACSM provides hydration guidelines to ensure you begin your exercise or race in a hydrated state.

  • Drink 5 to 7 ml per kilogram of body weight four hours before the race.
  • Drink another 3 to 5 ml per kilogram body weight two hours before the race.

As you can see, these are general guidelines and because they’re intended to cover a variety of sports, particularly weight class sports like wrestling and judo, you’d need to adjust as you feel necessary.  For most triathletes the guidelines are probably more important for day-to-day training than race morning.  Because based on my experience standing in the long porta-potty lines race morning, being under-hydrated is not an issue.

During Race Hydration

The ACSM position paper acknowledges that for best results you need to know your sweat rate under various conditions.  Its focus is still on hydrating to minimize body weight loss during exercise.  Specifically, to avoid compromising your performance you should not lose more than 2% of your pre-exercise body weight due to dehydration.  Also, thirst alone is not a good indicator of when to drink, particularly for older athletes, because your ability to detect thirst from dehydration diminishes with age.

The ACSM also encourages the consumption of electrolytes, particularly sodium and potassium.  The paper states that the primary purpose of electrolyte consumption is to stimulate thirst and retain fluids while replacing some of the electrolytes lost in sweat.  Here is the specific guideline:

  • For marathon distance events consume .4 to .8 liters of fluid per hour.  Consume closer to the lower end of the range if you’re a slower and/or smaller athlete or competing in cool conditions.  Consume closer to the higher end of the range if you’re a larger and/or faster athlete or you’re competing in hot humid conditions.

Post-Race Hydration

Post-race recommendations are intended to rehydrate your body and compensate for body weight losses

  • Consume 150% of the body weight lost over six hours, or 24 ounces of fluid for every pound lost or 1.5 liters/kilogram.
  • Consume salty food or sports drink containing electrolytes to replace lost electrolytes.

The drink ahead of thirst approach and its hydration prescription has provided the foundation for long course race hydration for many years.

However, this philosophy is now being challenged by the complete opposite strategy of drink to thirst.  The first strategy says that if you wait until you’re thirsty it’s too late; you’re already on your road to dehydration.  The latter strategy says to follow your innate sense, drink only when thirsty.

Tim Noakes Position:  Drink to Thirst

Supporters of this theory, which includes some very prominent coaches, believe you should drink only when thirsty and not attempt to replace all fluid lost to sweat.  Their rationale is that you should follow the wisdom of your body because its thirst mechanism was developed over thousands of years.   They believe that the percentage of dehydration and subsequent body weight loss is less important since there’s such a large variation in the ability of individuals to tolerate different levels of dehydration.  Here are some of the key components of this theory:

  • The body is more focused on homeostasis or in other words the concentration of body fluids as opposed to weight.
  • The electrolyte concentration in your body is significantly higher than the electrolyte concentration in even a salty sweater’s fluid loss. The body’s sodium concentration is approximately 140 mmol per liter while the sodium concentration in sweat is approximately 20 to 60 mmol per liter.
  • Since the fluid loss from sweating is greater than the electrolyte loss, the electrolyte concentration in your body increases.  Initially this increase activates the release of ADH, which is a hormone that signals your kidneys to restrict urine output to conserve fluid.  As you continue to dehydrate, your body’s thirst mechanism will kick in so you’ll consume fluid to rebalance your body’s fluid concentration.
  • If you follow the drink to thirst process you do not need to consume electrolytes.  Since the sodium concentration in your body increases as you sweat there’s no advantage to consuming additional electrolytes.  The disadvantage is that you’re likely to over consume fluids because the sodium in the drink will encourage you to drink more, which will drive your concentration lower…in the extreme the result would be hyponatremia

The key recommendation is don’t try to drink to match your sweat rate.  Focus on drinking to thirst, which is anywhere from 30% to 60% of your sweat rate.

So now what should you do?

If you’re feeling a little confused don’t sweat it.  Even the experts are struggling to come up with what the real guideline should be.  And the fact is there’s no one answer that’s right for you in every situation.

Here is a practical approach that I use for figuring out how to properly hydrate for triathlon training and racing:

Weigh yourself: 

Step 1:  To get a handle on your sweat rate, at least once a week weigh yourself before and after a training session.  Keep a log so you can track the changes in your weight.  One hour runs or bike trainer sessions (be sure to use a fan) work best because don’t need to drink much.  If you do consume fluid be sure to adjust for it when you determine your sweat rate.  If possible, jot down the air temperature in your log to get an idea of how it affects your sweat rate.  This will give you your sweat rate per hour.

Step 2:  Once you know your sweat rate, you have a good idea of how much to take in to replace what you lost.  The goal ISN’T to consume ALL of your lost fluid during the race, but to consume enough to maintain performance without stressing your digestion.  For me, I like to replace between 50-80% of what I lose on the bike, and 30-50% on the run.

Remember for calculation purposes 1 pound is equal to 16 fluid ounces or .95 kg is equal to a liter.  This isn’t perfect science but it’s simple and pretty effective.

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 your hydration needs to be adjusted up or down, respectively to match your pace to the conditions.

Keep your head in the race:  you thirst mechanism was developed over thousands of years of evolution but your race emotions weren’t.  Do your best to stay calm and focused.  Set up cues, such as a watch that goes off every 15 or 30 minutes, if needed to remind you to check-in on your hydration status regularly during a race.  Always remember the number one rule, especially for long course triathlon racing, is to take care of yourself at all times.

That’s it for this week.  Until next time train safe, stay healthy, and hope to see you at the races.

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