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INDIVIDUALIZED HYDRATION PLANS FOR ULTRADISTANCE ENDURANCE ATHLETES

Corcoran, Michael Ph.D.; Ayotte, David Jr M.S., CSCS, CPT, USATF

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ACSM's Health & Fitness Journal: 7/8 2019 - Volume 23 - Issue 4 - p 27-31
doi: 10.1249/FIT.0000000000000490
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Abstract

INTRODUCTION

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Hydration and sports performance is a topic that has been well covered. Rather than reinvent the wheel, the purpose of this article is to review what a tailored hydration plan looks like and when it might be advantageous to create one in an effort to maximize athletic performance. In general, the longer and harder an endurance event, the more it makes sense to have a good, well-thought-out hydration plan in place.

What does a good hydration plan look like? It is an approach that takes your unique sweat rate (fluid loss and sweat composition) and uses this information as a guide for what kind of fluid you should consider consuming, how much, and how often to maximize your performance.

What does a good hydration plan look like? It is an approach that takes your unique sweat rate (fluid loss and sweat composition) and uses this information as a guide for what kind of fluid you should consider consuming, how much, and how often to maximize your performance.

If you are planning to participate in an ultradistance endurance event such as an Ironman triathlon or 100-mile ultramarathon, a well-thought-out hydration plan can be the difference between a did not finish (DNF) and setting a personal record (PR). Although not mainstream, these events are becoming increasingly common. Consider that in 1999, there were about 1,500 participants at Ironman USA Lake Placid. In 2018, there were about 2,800 entrants. Other events show similar trends. The ability of athletes to hydrate appropriately for these events is crucial. A good hydration plan should ensure adequate hydration, before, during, and after (rehydration) an event. This article is focused on hydration during the event with the assumption that the individual begins the event hydrated. Regarding preexercise fluid intake, consuming 16 ounces of a high-sodium beverage (roughly 1,500–3,000 mg/L of sodium) 45 to 90 minutes before an event has been found to improve performance, particularly during events taking place in warm climates (1). See the Table in this article for a general guide on whether a tailored hydration plan is worthwhile based on your activity.

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Figure:
Photo courtesy of Michael Corcoran.
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TABLE:
Determining Hydration Needs Based on the Duration of Activity

DEVELOPING A HYDRATION PLAN: WHAT GOES INTO IT?

Two major components are necessary in the development of an effective hydration plan: (a) Determine the individual’s rate of fluid loss during activity (How much should I drink?), and (b) determine the electrolyte composition of the individual’s sweat (What kind of beverage is optimal for me?).

How Much Should I Drink?

Not too much, not too little. Athletes who lose as little as 2% of their body mass through exercise-related sweat loss tend to exhibit reduced awareness and coordination, power output, and overall endurance (3). Conversely, overhydration, which occurs when an individual consumes more fluid than they lose, also can lead to reduced performance. Signs of overhydration include frequent bathroom trips (a sure way to lose time), weight gain during the event, stomach upset, and, at the most extreme, exercise-associated hyponatremia (EAH) (4). EAH is unlikely to happen except in instances whereby an individual is competing in an ultraendurance event and consumes hypotonic fluids in excess of fluid losses.

The key with a successful hydration plan is to consume just enough fluid, electrolytes, and energy to sustain your pace while avoiding stomach upset, bonking, weight gain, heat exhaustion, and the many other issues associated with a suboptimal hydration state (3).

The key with a successful hydration plan is to consume just enough fluid, electrolytes, and energy to sustain your pace while avoiding stomach upset, bonking, weight gain, heat exhaustion, and the many other issues associated with a suboptimal hydration state (3).

How to Determine Fluid Loss (i.e., Sweat Rate)?

  • Step 1. Choose a moderate to hard and relatively long training session that is ideally performed in conditions similar to those in which you will be racing/competing. The session should preferably last at least 75 minutes but be logistically feasible for the completion of the other steps of this protocol below.
  • Step 2. The volume of fluid consumed (ounces) during the training session must be recorded. For accurate measurements, do not ingest any solid foods. Use premeasured bottle(s) containing your usual training beverage of choice. Do not spit out any of the liquid during the training session.
  • Step 3. Immediately before exercising, you should void your bladder and obtain your nude weight. Record this as the preexercise weight. The climate, as well as the time that you begin training, should be recorded as sweat rates can vary by as much as threefold when testing in cooler (less than 40°F [4.5°C] and warmer weather (90°F [32°C] or higher). After this, complete your training session.
  • Step 4. After you complete your training session, record the stop time of this training session, void your bladder, towel dry, and obtain your nude weight. Also, record the amount of fluid you consumed during the training session by subtracting the fluid remaining in your bottles from the amount with which you started.
  • Step 5. Calculate fluid losses using the numbers you recorded (pretraining weight, posttraining weight, pretraining fluid volume, and posttraining [remaining] fluid volume). See the case study for an example of how to do this calculation.

What Type of Fluid Should I Drink?

A major consideration to what kind of fluid an athlete should consume is whether the beverage is providing a sufficient amount of electrolytes. Besides water, sweat consists of trace amounts of minerals (mainly sodium chloride [table salt], but also tiny amounts of potassium, calcium, and magnesium).

There are several benefits to including sodium in a sports beverage for prolonged endurance activities. These benefits include the maintenance of serum electrolyte concentrations (6) (which in turn may help in preserving neuromuscular coordination and power output) (7), increased thirst as well as reduced urine output (which in turn helps maintain whole body fluid balance) (8), and more efficient glucose absorption from the gut (5).

Case Study: Sweat Rate Calculation for a Long-Distance Runner

Kayla went out for a 2-hour run (outdoors, warm temperature at 83°F [28°C], 55% humidity). During this run, she managed to consume 8 oz of fluid. Her prerun bodyweight was 126 pounds. After returning from her run, she now weighs 123 pounds. To calculate her fluid loss:

  • Note: 1 pound is 16 oz
  • Bodyweight loss = 126–123 = 3 pounds. This equates to 3 × 16 = 48 oz of fluid lost.
  • However, we need to account for what Kayla consumed during training too (8 oz or 0.5 pounds).
  • Total sweat loss = 3 + 0.5 pounds. In total, Kayla lost 56 oz (16 oz/pound × 3.5 pounds total).
  • This equates to an average sweat rate of 0.5 oz every minute (56 oz/120 minutes).
  • From a practical perspective, because it is recommended to consume fluids every 10 to 20 minutes of prolonged activity, using a 15-minute drink interval for this example, Kayla is losing about 7 oz of fluid every 15 minutes.

Consuming 7 oz of fluid every 15 minutes during her run, however, may not be practical. This volume of fluid (almost a full cup) may be too much to tolerate. Therefore, it is good practice to take more of a “barn door” approach rather than a “bull’s-eye” approach. Calculating a fluid intake range is a more practical strategy. A range also leaves room for error. Being overly precise can be counterproductive. In the midst of a competition, the last thing you want to do is panic because you did not consume x oz of fluid at a specific time interval. In the above scenario, in theory, if Kayla drinks about 7 oz of fluid every 15 minutes during her next scheduled 2-hour run (under similar conditions), she would be expected to lose little to no weight (i.e., remain fully hydrated). Any more fluid than this would result in overhydration and is unnecessary. Therefore, this amount should be the maximum she should consume. But how about the minimum? Research on dehydration has indicated that losing more than 2% of one’s bodyweight leads to a significant deterioration in one’s athletic performance, particularly in hot and humid conditions (3). The minimum that Kayla should consume can be determined by what 2% of her bodyweight would be, converted to ounces of fluid and broken down into manageable and practical time intervals. In this scenario, 2% of Kayla’s pretraining bodyweight is 126 × 0.02 = 2.5 pounds (or about 40 oz of allowable sweat loss). Because she lost 56 oz, to avoid exceeding a 2% bodyweight loss, she’ll need to drink 16 oz during her 2-hour run. This equates to consuming about 2 oz every 15 minutes of activity, which may be much more manageable for her.

To make things a bit simpler than thinking about ounces of fluid, it can be helpful to view hydration in terms of “sips.” For reference, a typical sip of fluid is about 1 oz (although this can vary a bit from individual to individual). Asking an athlete to consume two sips of fluid every 15 minutes is usually a simple approach to follow. For Kayla, her range would equate to 2 to 7 sips of fluid every 15 minutes. If she can tolerate seven sips during her run session, terrific. If she can only tolerate two sips, then that’s fine too. Remember, never, ever try anything new on race day. Kayla should experiment with this range in training and do what works best for her (and her gastrointestinal system). If this appears to work well for this athlete, then this is one less thing for her to think about on race day.

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Figure:
Photo courtesy of Michael Corcoran.

There are several benefits to including sodium in a sports beverage for prolonged endurance activities. These benefits include the maintenance of serum electrolyte concentrations (6) (which in turn may help in preserving neuromuscular coordination and power output) (7), increased thirst as well as reduced urine output (which in turn helps maintain whole body fluid balance) (8), and more efficient glucose absorption from the gut (5).

Regarding the latter, the longer glucose remains in your gut, the more likely you are to suffer from gastrointestinal issues (the carbohydrate will draw water into the GI tract resulting in diarrhea).

With the recognition that adequate sodium replacement during competition can have a significant impact on race performance, sweat sodium testing is becoming increasingly popular. There are several ways to measure how much sodium is lost through sweating, although these methods often require relatively expensive equipment and someone who is well trained in the procedure. If you are interested in getting a sweat sodium measurement, you can contact your local college or university to see if they offer such a service. Alternatively, many endurance coaches may either offer this service or be able to direct you to someone who can do this test for you. The good news with this assessment is that sweat sodium levels are genetically determined, meaning that you usually only need to get tested once (9).

As to what to expect, the sodium concentration in sweat can vary among individuals by almost tenfold (from 200 to 2,000 mg/L) (2). To put this in perspective, male and female athletes lose, on average, 1 to 1.5 L of fluid per hour when ambient temperatures are between 60°F (15°C) and 98°F (37°C), 50% humidity (2). This means that an athlete competing in a 5-hour endurance event could lose up to 15,000 mg of sodium. Clearly, there are issues with a one-size-fits-all approach to hydration. Many sports drinks are “light” on sodium and, thus, are not ideal for individuals with heavy training demands. See the Figure, which was adapted from two recent studies that examined sweat sodium losses in athletes (2,10). You will notice that the amount of salt lost through sweat by many athletes is higher than what would have been replaced by a common sports drink.

Case Study: Individualized Hydration Plan for a Long-Distance Runner

In applying sodium testing to our runner (Kayla), let’s assume she is sweat tested and her sweat sodium concentration is determined to be 1000 mg/L. Let’s also assume that she was consuming a typical sports drink during her run, which contained 270 mg of sodium in the bottle (591 ml total); 270 mg/591 ml is about 460 mg/L or about half of what she is losing. On the basis of her sweat test, Kayla may wish to add a quarter teaspoon of table salt to her bottle. Her plan is thus to consume two to seven sips of her sports drink (that was supplemented with a quarter teaspoon of table salt), every 15 minutes of her run. If this is not practical for her and she knows that a certain sports drink will be offered at her race, she can plan accordingly. Carrying a few salt tablets in your pocket and consuming them periodically with the beverage offered on the race course may be a more suitable alternative (6). Remember, however, to never, ever try anything new on race day. Practice, practice, practice.

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Figure:
Photo courtesy of Trevor Bennion, DHSc, www.portraitscientist.com.
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Figure:
Photo courtesy of Trevor Bennion, DHSc, www.portraitscientist.com.
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How much sodium do athletes lose through sweat?

Many manufacturers produce sports drinks targeted for endurance athletes, which contain higher amounts of sodium, usually 800 to 1,500 mg/L. Opt for these drinks if a sweat sodium test indicates that you are losing this much salt. However, this level of sodium may not be necessary for you. Too much salt in your drink can potentially lead to GI distress, reduced beverage palatability, and water weight gain, none of which are helpful. Conversely, if you are a high-salt sweater and the race you are competing in only offers standard sports drinks, you may do well to bring your own beverages if possible or consider consuming a source of sodium, such as from solid food, gels, or salt tablets, to make up the difference. Should you choose to add salt to a beverage, a quarter teaspoon of table salt contains approximately 400 to 500 mg of sodium. Note: As with fluid volume, there is no need to be exact with your sodium addition. If, through a sodium sweat test, you find that you are losing 1,215 mg of sodium per liter of sweat, getting your sports drink reasonably close (1,000 mg or one-half teaspoon, for example) is sufficient. Overall, a sweat sodium test can help eliminate much of the guesswork when determining which beverage is right for you.

BRIDGING THE GAP

For athletes competing in long-distance endurance races, a well-thought-out and individualized hydration plan may make the difference between not finishing and setting a personal record. The creation of such a plan requires knowledge of one’s sweat rate under certain conditions as well as how much sodium is lost in this sweat. These two variables will help in determining what to drink and how much. Should you decide to create a tailored hydration plan for yourself, make sure to practice with this plan during training, preferably under conditions similar to what you expect to face on race day.

References

1. Mora-Rodriguez R, Hamouti N. Salt and fluid loading: effects on blood volume and exercise performance. Med Sport Sci. 2012;59:113–9.
2. Baker LB, Barnes KA, Anderson ML, Passe DH, Stofan JR. Normative data for regional sweat sodium concentration and whole-body sweating rate in athletes. J Sports Sci. 2016;34(4):358–68.
3. Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine Position Stand: exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377–90.
4. Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clin J Sport Med. 2015;25(4):303–20.
5. Jeukendrup A, Carter J, Maughan R. Competition fluid and fuel. In: Burke L, Deakin V, editors. Clinical Sports Nutrition. Australia: McGraw-Hill Education Pty Ltd.; 2015. p. 377–419.
6. Del Coso J, González-Millán C, Salinero JJ, et al. Effects of oral salt supplementation on physical performance during a half-ironman: a randomized controlled trial. Scand J Med Sci Sports. 2016;26(2):156–64.
7. Coso JD, Estevez E, Baquero RA, Mora-Rodriguez R. Anaerobic performance when rehydrating with water or commercially available sports drinks during prolonged exercise in the heat. Appl Physiol Nutr Metab. 2008;33(2):290–8.
8. Shirreffs SM, Maughan RJ. Volume repletion after exercise-induced volume depletion in humans: replacement of water and sodium losses. Am J Physiol. 1998;274(5 Pt 2):F868–75.
9. Brown MB, Haack KK, Pollack BP, Millard-Stafford M, McCarty NA. Low abundance of sweat duct Cl- channel CFTR in both healthy and cystic fibrosis athletes with exceptionally salty sweat during exercise. Am J Physiol Regul Integr Comp Physiol. 2011;300(3):R605–15.
10. Lara B, Salinero JJ, Areces F, et al. Sweat sodium loss influences serum sodium concentration in a marathon. Scand J Med Sci Sports. 2017;27(2):152–60.
Keywords:

Hydration; Ultradistance Endurance; Sweat Rate; Electrolytes; Athletic Performance

Copyright © 2019 by American College of Sports Medicine.