Getting ready to go long at my first marathon.
Lets start out with a few scenarios. You are a runner and decide to enter the West Wyoming marathon. You are a cyclist and decide to enter a local metric century. You are a triathlete and decide to move up to an Olympic distance event.
You show up at the marathon and weather conditions are cooler and less humid than the average for your training runs. Plus its overcast and windy. Not surprising considering that Wyoming is drier and windier than most of the United States. You get to the metric century and weather conditions are way hotter than your average training rides, and the sun is beating down like a blacksmith pounding out a horseshoe. You arrive at the triathlon to find that the weather is nice, much like your average training conditions but you haven’t been feeling well the last week or so and haven’t been eating or drinking quite as much as normal. Also aid stations have a different sports drink than you were expecting.
Now a few questions. How would the above scenarios affect your hydration plan? How did you come up with your hydration plan? How will you evaluate your hydration plan during the race/event? Does your hydration plan match your race outfit?
Now let’s talk about you for a minute. Do you sweat a lot, a little, about average? Have you ever weighed yourself before and after exercise to gauge your sweat rate? Do you prefer sports drinks or are you a water purist? How would you know if you were becoming dehydrated? Do you worry about hyponatremia?
I know what you are thinking. Gee that’s a lot of questions big guy, any chance there will be answers at some point. Let me reply to that in the form of a weather forecast: guidelines and resources with a chance of occasional answers.
What I’m getting at is that hydration is a tricky subject. There are many myths and misconceptions and even the experts are not in close agreement. If you check the hydration position statements at the end of this post you will find two groups advocating drinking set amounts of fluid during set amounts of time if possible. The third group suggest using thirst as a guide to when to take on more fluid. All seem to agree that a fluid loss equal to 2% or more of body weight is what we are trying to avoid.
While our first priority is to avoid dehydration, we also need to be aware of hyponatremia or an abnormally low level of sodium in the blood. The most common cause of exercise-associated hyponatremia (EAH) is excessive fluid intake. Hyponatremia is a growing concern because more people are doing marathons and triathlons. Back of the pack athletes like myself need to be especially aware of hyponatremia given our long time out on the course.
I found the quote below from a paper on exercise-associated hyponatremia particularly chilling. A link to the full paper is in the resources section.
“For example, in the 2002 Boston Marathon, Almond et al found that 13% of 488 runners (63 runners) studied had hyponatremia (defined as a serum sodium concentration of 135 mmol/L or less) and 0.6% (3 runners) had critical hyponatremia (serum sodium concentration of 120 mmol/L or less).”
Lessons From Little Rock and Chicago Marathons
I found two studies on PubMed that illustrate current attitudes and knowledge base about hydration among recreational athletes. Both are surveys of marathoners and were published in 2011. So let’s get started with the first in our science cited series with a look at highlights from each study.
Half-Marathon and Full-Marathon Runners’ Hydration Practices and Perceptions
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3418934/
The authors surveyed runners participating in the 2010 Little Rock, Arkansas, Half-Marathon and Marathon. They spent a lot of time and effort in developing their 23 question survey and gathered a lot of useful data. They separated the runners into three groups – low, mod, high – based on running volume, expected race completion time, and racing experience. A total of 146 men and 130 women were included in the final sample. Both half marathoners and marathoners were included.
The authors felt that their most important finding was that during training 70% of survey participants reported “decreases in running performance thought to have been caused by dehydration.” Further 45% reported suffering heat-related illness symptoms that they thought were caused by dehydration.
Only 20% of survey participants reported monitoring their hydration status. The methods runners said they used to monitor hydration status included urine color, pre-planning amount of fluid to be consumed or intervals at which to drink, frequency or volume of urination, thirst and listening to body, dehydration-induced symptoms (e.g., “lack of sweating,” “calf cramps,” dry skin, chapped lips, “hand moisture”), sweat rate, skin turgor test (pinch test), change in body weight, and total body water measurement predictor tool.
The authors noted three key points in their report:
1. Most runners had experienced performance decrements that they attributed to dehydration. Almost half the runners had sustained heat-related illness symptoms that they related to dehydration.
2. Despite these adverse events, few participants monitored their hydration levels or used specific hydration plans.
3. Better dissemination of accurate scientific information about appropriate hydration practices may increase runners’ safety.
Lack of Awareness of Fluid Needs Among Participants at a Midwest Marathon
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3445216/
The authors of this study like those above surveyed marathon runners. In this case at the 2007 LaSalle Bank Chicago Marathon. In this survey runners were asked about injuries as well as hydration. They were also asked if they had ever been treated in the medical tent during or after a marathon. A total of 419 runners completed the survey: 211 women and 208 men. Below are three paragraphs that I think reveal most of the information most important to the topic of discussion today.
“Of the 278 survey participants who had completed a marathon, 54 (19.0%) had been a patient in a medical tent: 17 (31.5%) for dehydration, 10 (18.5%) for cramping, 9 (16.7%) for dizziness or passing out, 6 (11.1%) for musculoskeletal issues, 5 (9.3%) for vomiting, 3 (5.6%) for bleeding, 3 (5.6%) for heat or cold related illnesses, and 1 (1.9%) for hyponatremia.”
“Most runners reported no knowledge of their sweat rate (n = 370, 88.7%), and the majority did not weigh themselves to assess hydration status (n = 284, 67.8%). Furthermore, 335 (81.3%) did not address hydration status; 77 (18.7%) used other methods; and 38 (49.3%) used urine color. The other methods of hydration assessment were thirst (n = 9, 11.7%), distance (n = 3, 3.9%), past experience (n = 3, 3.9%), “scale” (n = 2, 2.6%), general feeling (n = 2, 2.6%), and frequency of urination (n = 2, 2.6%); pulse, cramping, amount drank, “sweat,” and “pinch test” were all listed once (1.3%). Finally, 265 runners (60.1%) supplemented their fluids with carbohydrate, 86 (19.5%) with electrolytes or salt tablets, 68 (15.4%) with caffeine, and 22 (5.0%) with supplements.”
“An athlete should replace 50% to 80% of their sweat losses to maintain an adequate blood volume and appropriate core temperature during endurance exercise. On average, marathon runners complete the race with 3% to 4% dehydration and replace less than 50% of their sweat losses. Self-weighing may be most useful in determining when individuals have hydrated too much. It is a worrisome sign to maintain or gain weight during a marathon, owing to the potential for exercise-associated hyponatremia.”
The authors concluded:
“The majority of runners (in their survey) were inexperienced marathoners, lacked concern about musculoskeletal injury or hyponatremia, and did not use methods to assess their hydration status.”
My conclusions from reading both studies:
- Weigh yourself. Go exercise. Weigh yourself again. Calculate fluid loss. There I said it. Repeat periodically and for different weather conditions. Keep a record of your findings.
- You need to have a method or methods to evaluate your hydration status during training and events. You need to practice them and refine them over time.
- Hydration needs vary with the individual, conditions and exercise intensity. Your hydration strategy should take these factors into account.
- Both surveys had quite large sample sizes which supports the conclusions reached. At the same time, both surveys rely on self reporting which cannot be considered as reliable as double blind testing.
A few closing notes. I have hidden an Easter egg (hidden message) in this post. The first person to find it and post a comment about it wins a prize. Also I would love to hear comments from anyone who is trying mindfulness meditation for the first time. Finally let me encourage you to follow me on twitter @swimbikestumble.
Resources:
Hyponatremia
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001431/
Exercise-Associated Hyponatremia
http://cjasn.asnjournals.org/content/2/1/151.long
American College of Sports Medicine position stand. Exercise and fluid replacement
http://journals.lww.com/acsm-msse/Fulltext/2007/02000/Exercise_and_Fluid_Replacement.22.aspx
National Athletic Trainers’ Association Position Statement: Fluid Replacement for Athletes
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1323420/pdf/jathtrain00002-0094.pdf
Updated Fluid Recommendation: Position Statement from International Marathon Medical Directors Association (2006)
http://aimsworldrunning.org/articles/IMMDA_Updated_Fluid_Recommendation.pdf
Skin Turgor: One indication of hydration status
http://www.nlm.nih.gov/medlineplus/ency/imagepages/17223.htm
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