Hydration on during endurance events

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Hydration on during endurance events

Postby ssorrow » Wed May 11, 2011 12:18 pm

I'm looking for guidance on an issue I faced in the St George Ironman which ultimately caused me to drop halfway through the run. I have completed 2 prior Iron distance events and multiple 50 mile runs in hot conditions and never had as significant reaction as I did in St George. I was very lethargic and spaced out for the majority of the run.

I have a high sweat rate of approx 48-60 oz per hour depending on the heat and until now I have followed a philosophy of consuming the same amount of liquids per hour to match my sweat rate and pairing it with electrolytes.
I performed heat training in the months preceding to prepare for the conditions.

After reading the Hammer article on Hydration I have questions on how to maintain my hydration in hotter environments ... ge-section

1 - If the maximum liquid a person can absorb in an hour is approx 33 oz then what alternatives would a person with a high sweat rate have to maintain a 10-14 hour race.
Options as I understand them would include
splashing and misting with water
using ice to cool down
stopping or reducing intensity to reduce core temperature
additional heat training

I assume the methods above only partly solve for this and knowing that a loss above 5% of body weight to sweat will compromise health and seriously compromise performance I'm mainly seeking some way to complete longer events.
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Re: Hydration on during endurance events

Postby steve-born » Fri May 20, 2011 1:05 pm

Hello ssorrow -

My apologies for not replying to your post sooner... I was out of town for about a week and a half and am now just getting caught up with emails, etc.

Anyway, I wanted to ask you how you ascertained your sweat rate of 48-60 oz per hour. Did you have a test done indoors under controlled conditions for an hour or two? The reason I ask is because oftentimes these one to two hour "sweat tests," while helpful, don't necessarily reflect what the body will do in a much longer bout of exercise under non-controlled conditions.

Put another way, if you put someone on a stationary bike or a treadmill for an hour or two, inside a room and under controlled conditions (such as not having a fan, which would simulate the wind blowing against your skin, which would help support the body's evaporative cooling mechanisms) that person is going to sweat an awful lot while also losing quite a bit of sodium at the same time... I know I would!

So the burning question is: Will the body continue to lose fluids and sodium at the same rate hour after hour? In other words, if you lose 48 oz of fluid and 2 grams of sodium per hour after doing a one- or two-hour sweat test, indoors and under controlled conditions, does that mean that the body will continue to lose those same amounts during longer bouts of exercise and in a non-controlled environment?

My answer is that, with very few exceptions, the body will not lose fluids and sodium at the same rate, and the reason for that position is because the body has a number of built-in hormonal mechanisms (survival mechanisms, if you will) that help to prevent losses from continuing to be of high volume hour after hour.

I guess what I'm saying is that while these sweat tests can be helpful, I do not believe that they reflect what your body is able to comfortably accept in return when you exercise. Another example is calorie depletion. During exercise, the body will burn upward of 800 calories an hour. However, the body is simply not equipped to accept anywhere near that many calories in return from one's fuel donation. What "bridges the gap" between what you're burning calorie-wise and what your body is comfortably able to accept from your fuel donation is the thousands of thousands of calories available from body fat stores. In fact, once you hit hour #2 and beyond, about 2/3 of your energy requirements will be fulfilled from body fat stores.

That's why you don't have to replace "X" out with "X" or "near-X" back in when it comes to calories. I firmly believe that this is also true when it comes to fluids and electrolytes as well... the body has a number of mechanisms already built in that help "bridge the gap" between what you're losing and what your body can comfortably accept in return.

As you've probably read in one of the articles on our website, most of the cases of dilutional hyponatremia occurred when athletes routinely and consistently consumed over a liter of fluid an hour (about 34 ounces). Now, that doesn't necessarily mean that one can't consume that much on an hourly basis; however, if you do get up into that liter-of-fluid-an-hour amount, or higher, you need to exercise caution in doing so and you will need to increase your electrolyte intake to match your increased fluid intake.

Dr. Ian Rogers once wrote: "While the old mantra, 'If you don't drink you die' is not yet dead, it has certainly been challenged. We can no longer assume that excess fluid taken during prolonged exercise will just be passed out in the urine. Like most things in life, balance is the key and the balance is likely to be at a fluid intake not much above 500 mls per hour in most situations, unless predicted losses are very substantial." (500 mls = about 17 ounces).

What I'm hopefully getting at is that you may very well be one of these athletes who needs more fluids than what the average athlete needs... you might be one of those athletes who Dr. Rogers refers to as being one whose "predicted losses are very substantial." If that's the case, I don't have a problem if your fluid intake is above the norm and even a bit beyond what is generally suggested as the upper limit for most of us, which is about a liter an hour. As long as your electrolyte intake increases to match your fluid intake, you should be just fine.

What I would caution against is placing too much emphasis on what a sweat test results indicate... as mentioned earlier, they don't necessarily reflect what the body will do hour after hour during a lengthy race. Again, if you feel that you need upwards of 33-34 ounces per hour, perhaps slightly more, that's OK, and I would suggest you start with that. But remember that you can run into some real serious problems if you're trying to replace all of the fluids you may (key word "may") be losing. You will run into some real serious problems with over-hydration, just as many as you would if you were dehydrated, which is why of all the components of fueling - fluids, calories, and electrolytes - fluid intake is the one that I believe has the most serious consequences.

Consuming 48-60 ounces of fluids hourly is really a huge amount and my concern is that you may be basing that intake on what a one- or two-hour sweat test is telling you. As I've already mentioned several times, while knowing what you're depleting is interesting and oftentimes helpful information, it doesn't necessarily reflect what your body is able to accept in return from you. If anything, I'd much rather see athletes err on the "too low" side when it comes to calories, fluids, and electrolytes, rather than trying to replace "X" out with "X" or "near-X" back in ("X" being what your body is losing). Fixing a "not enough" problem is so much easier than resolving an "uh oh, I overdid it with the fluids (or calories or electrolytes), now my stomach is rebelling, and I feel like crap" problem. As an example, if an athlete feels as though they're not getting in enough calories that's an easy problem to fix (you simply consume a bit more). However, if an athlete over-supplies the body with too many calories that's a much harder and longer-lasting problem to resolve... at the very least the stomach will be upset for awhile as the body tries to process those extra calories.

My suggestion is that if you are a heavy sweater then yes, consume fluids in amounts higher than our recommendations... you may very well need a liter of fluid an hour, perhaps even a bit more. Just remember to start on the low end (34 ounces/hour). And if you feel that it's not sufficient, increase the amount of fluids that you consume gradually. Lastly, make sure to increase your electrolyte intake as well.

I hope you will find my perspective and suggestions helpful.

Sincerely -

Steve Born
Fueling Expert
Event Sponsorship Coordinator
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