Monitoring Hydration Status, by Dr Kitima
Monitoring Hydration Status |
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Monitoring Hydration Status, by Dr Kitima
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Monitoring Hydration status:
At the start of every race or training session, we have a given volume of circulating blood in our body. That blood is parceled out to our muscles, our GI system, and other organs. Throughout the course of a HIM/IM or long training session, we all become progressively dehydrated through fluid losses (sweat, urine, vomit—hopefully not). The only way to replace those fluid losses is through our GI system. Once you have an i.v. in the medical tent, you day is done. In order for your GI system to absorb the necessary fluids during race, it must have adequate blood supply. So put simply: If you want to prevent dehydration, you must maintain GI blood flow. It’s not enough to just put sports drinks, water, gels, salt tabs in our mouth and swallow it. Our gut needs to have enough blood flow to it to absorb all those things. If not, then forget out watts, pace, PR’s because sooner or later dehydration ensues and you’ll be lying in a medical tent.
Maintaining adequate GI blood flow requires:
- Exercising at an intensity that doesn’t shunt blood from the gut---steady aerobic efforts. No spiking of watts on the bike. No running at tempo paces on the run.
- Staying relatively hydrated or not becoming too dehydrated.
- Keeping core body temperature from getting too high. When we get hot, blood flows to the skin to sweat and cool the body---blood that should be supplying muscles to exercise or the gut to process what we ingest.
- Ingesting dilute or not highly concentrated food/fluid. When you eat/drink something highly concentrated, the stomach pulls fluid from your body’s blood volume to dilute what is in stomach. Therefore, drink water after taking a gel or salt tablets---not sports drink!
Fluid losses during exercise is mainly through sweat and urine output. The one source of fluid loss that isn’t easily measured while on the race course is sweat. Sweat rate depends on air temperature, humidity, how acclimatized one is to that weather, and intensity of exercise. Knowing sweat rate for different conditions or for anticipated race conditions is important and can be determined by doing sweat tests during training. I highly recommend doing long runs, long rides, and race rehearsal in weather conditions that one would anticipate for race day, keep track of fluid and sodium intake, do a sweat test, and assess the amount of fluid/sodium intake is necessary for those conditions. For races with relatively consistent weather like IMFL, IMAZ, IMCoz, Kona (it’s either hot and humid or hotter and more humid on race day), it is important especially for those who live in cooler climates to train in hotter conditions (real or simulated with wearing extra clothes) to assess fluid and sodium needs as well as acclimatize. For races with variable weather such as IMLP, IMWI, IMC, IMCdA, then sweat tests and fluid/sodium needs should be assessed for a range of temperatures and conditions. (See Sweat test)
For me (trying to keep it simple), I know that for temps<72 degrees and regular NE humidity = 22 oz fluid/hour intake works well. For temps between 73-85, intake = 30 oz fluid/hour. For temps >86 degrees, intake > 40 oz/hour.
I have determined the above values through trial and error and doing sweat tests in those different temps during long rides and runs.
Urine output is a good way to monitor hydration status. I think (read: it’s my opinion---there’s no solid research on this subject) that you should pee large amounts at least every 2 hours in the first 4-6 hours of the race. Large amounts = enough urine to run down your legs and get your socks wet. After 6 hours, you should pee (in smaller amounts ) every 2.5-3 hours. If the urine output drops it, it’s time to increase fluid intake and cool yourself. If you need to slow down in order to process the increased fluid intake (see above about monitoring GI function), then please do so.
If it is possible for you to see the color of your urine (you’re a man and not peeing during the act of riding or running OR you’re a woman and there are white toilets to pee in on the race course), that will also help you assess your hydration status. Generally, the darker your urine is the more dehydrated you are. Ideally, peeing large amounts of clear urine means that you are relatively well-hydrated. Now if you are diabetic, have kidney problems, are on diuretics (and not caffeine. I’m talking furosemide, acetazolamide, HCTZ) then urine color and volume may not be as helpful in assessing hydration status.
The Sweat Test:
1. Weigh yourself before exercise that will last at least 1 hour.2. Note:
- the intensity of your exercise
- type of exercise (swim, bike, run)
- how much fluid you drank
- how much sodium you took during the exercise
- the conditions of the environment in which you exercised (104 degrees and humid summer in Arkansas vs. 70 degrees and dry)
3. Weigh yourself immediately after exercise.
4. Total fluid loss = Weight before minus weight after exercise + fluid consumed during exercise
- If you exercised your just 1 hour, that’s your hourly fluid loss for that exercise in that specific environmental condition.
- If you exercised >1 hour, you’ll divide the total fluid loss for an hourly sweat rate
- Fluid consumed: 16 oz of fluid = 1 pound. So to figure out how many pounds of fluid you consumed divide by 16.
For example, if I ran for an hour in 90 degrees and 80% humidity. I drank 8oz of Ironman Perform. I weighed 130 pounds before the run. I weigh 125 pounds after the run. My sweat rate calculations:
130 lbs - 125 lbs = 5 lbs + 0.5 lbs (which is 8oz divided by 16oz/lb) = 5.5 lbs of fluid loss in 1 hour
5.5 pounds x 16oz/pound = 88 oz
Sweat rate = 88 oz/hour in the above conditions of which I only replaced 8 oz. Of note, I consumed 190mg of sodium (that’s how much is in 8oz of Ironman Perform) during that hour. I noted I had muscle cramps. I’m thinking I’ll need more sodium per hour in those conditions the next time. I also noted that my urine was really dark after the run and I was lightheaded. I’ll need to drink more the next time too.
Another example, I did my race rehearsal ride (6 hours) in 72 degrees and low humidity. I weighed 130 pounds before the ride. I drank 48 oz of concentrated Infinit with 80 oz of water (filled the Speedfill twice)---so total fluid consumed = 128 oz. The total sodium content of Infinit was 3900mg. I weighed 128 pounds after the ride. So my sweat rate calculations:
130 lbs -128 lbs = 2 lbs + 8 lbs (128 oz divided by 16oz/lb) = 10 lbs of fluid loss in 6 hours
10 lbs x 16 oz/lb = 160 oz fluid loss in 6 hours
26.7 oz / hour sweat rate for the above conditions. I replaced my fluid losses much better this time as I only lost 2 pounds. My sodium intake was 3900mg/6 hours = 650mg/hour. I had no abdominal bloating, muscle cramps, and peed 3 times in large quantities on the bike.
Sodium:
The studies concerning the need for sodium supplementation during an IM are conflicting at best. I will not get into a debate about those studies here, but I’m always up for a lively discussion if you send me a PM or start a separate thread on it. As far as needing sodium supplementation during IM and long training sessions to prevent muscle cramps, the research again is confusing and inconclusive. In my personal experience, I do feel that I must supplement with sodium to prevent muscle cramps. One’s nutrition plan for race day is highly individual and you must find what works for you.As for as needing sodium to prevent hyponatremia (low sodium levels in the blood), I think that if you are going to drink large quantities of water or dilute fluid then you must supplement with sodium. Hyponatremia in the IM medical tent occurs often enough to make a good case for sodium supplementation.
How much sodium does one need? The range of sodium content in sweat is very large: 300mg to 1500mg per liter. The only way to precisely know how much sodium you are sweating out is to take some of that sweat and send it to a lab to be measured for sodium levels. Basically, you’re estimating. The EN race nutrition guidelines recommend sodium intake to be 500mg-1000mg per hour which is a good place to start. I let muscle cramps be my guide for increasing the sodium intake. In temps less than 72 degrees, I know that 650 mg of sodium is enough for me because during all my long runs/rides/races I have not had a muscle cramp or swelling with that much sodium intake. In temps greater than 72 degrees, I need at least 990mg of sodium or I’ll have get terrible leg cramps. I used S!caps because there are 341mg of sodium per capsule compared to 40mg per capsule in Endurolytes. I simply didn’t want to be taking handfuls of pills/capsule to get my sodium during a race/training.
If you don’t have leg cramps, you still should take sodium with your fluid intake to prevent hyponatremia and dehydration. The American College of Sports Medicince recommendation for sodium content in fluids to replace athletes exercising for a prolonged period of time is 500-900mg per liter---which is 358-500mg per 24 oz (again size of average water bottle). This recommendation doesn’t appear to be backed by a specific study. I recommend erring toward the higher amount of sodium intake.
Troubleshooting:
GI shutdown:
The symptoms of GI shutdown are:- increased burping
- regurgitation or reflux
- abdominal bloating
- nausea
- decreased or no passing of flatus
- vomiting
Dehydration (see below) is a common cause of GI shutdown. So is increasing the intensity of exercise to the point of shunting blood to away from the GI to the muscles. Typically you can rescue yourself from increased burping, reflux, nausea, and bloating by slowing down/decreasing intensity of exercise, increasing intake of dilute fluid in small amounts, cool the body. Once the GI system has adequate blood supply you will stop burping so much and the gas in your gut (bloating) will pass either through the northern or southern end. At that point, you can resume your exercise intensity but do it slowly. If you absolutely can’t keep anything down, then the best you can do is really slow down and cool yourself and wait until what little blood supply you have is re-shunted to the gut.
It may sound like a lot to keep track of, but it’s not. You ask yourself:
When did I pee last? Was it a lot? Am I burping/getting nauseous/bloated?
In the same way that you pay attention to race nutrition, you pay attention to how you are absorbing that nutrition. When you cannot absorb what you are putting in your gut, you do everything you can to increase blood flow to the GI system. Easy peasy and so so important. There’s no point in having a nutrition plan if you can’t absorb it.
Dehydration:
The first symptoms are- dry mouth/sticky saliva
- reduced urination with dark/concentrated urine
- fatigue
The next stage will present with
- even more dryness in the mouth
- further decrease in urination with really dark urine
- increased heart rate
- decreased appetite
- slight dizziness
- cold hands and feet
Severe dehydration presents with
- changes in mental status
- more dizziness/lightheadedness
- inability to get up and walk
- further increased heart rate
- increased respiratory rate
- then loss of consciousness.
Hopefully, by monitoring your urine output you will not have any of these symptoms. If you do find yourself dehydrated, the only way to rehydrate yourself and still stay in the race is by drinking fluids and having your GI system absorb it. So slow down or even stop, cool your body, take small amounts of dilute fluids frequently. If you get to the point of needing i.v. fluids, your day is done.
Hyponatremia:
The problem is too much water and too little sodium = HYPONATREMIA (low sodium levels in blood). The early symptoms are- nausea/vomiting
- headache
- lethargy
- fatigue which then progresses to muscle spasms/cramps/weakness
- irritability
- seizures
- lastly decreased consciousness then coma.
In the IM medical tent, people with hyponatremia will present will the above symptoms and sometimes profound mental status changes. One year at IMLP, a guy was pulled off the bike course with hyponatremia. He laid in the medical tent cot on his back with his feet in the air pedalling because he thought he was still on the course. Most hyponatremic athletes in the IM med tent will have weight gain and some swelling. The treatment is to have them take in salty foods or salt tablets until they start peeing. Unconscious patients or those unable to eat are sent to the hospital to be closely monitored and have their serum sodium levels increased slowly (if severe hyponatremia is corrected to quickly, the brain herniates).
The key to avoiding hyponatremia is to not over-hydrate--before the race and during the race and to replace sodium lost through sweat and to take enough sodium when hydrating.
Putting all together:
1. During long rides/runs and non-A races, keep track of:- temperature, humidity
- hourly intake of fluid, calories, sodium
- Do a Sweat test and assess hourly sweat loss and how well you kept up with those fluid losses.
2. From the above data, formulate a nutrition/hydration plan (as per EN race nutrition guide in the wiki) for your race rehearsal. You can and should practice this plan on long ride and runs. My plan for IMWI looked like this:
- For temps under 72 degrees, I shall take 250 Cal/hour, 650 mg sodium/hour, 24 oz fluid/hour.
- For temps between 72-80 degrees: Caloric intake remains the same or decreases depending on GI status, increase sodium to 900mg/hour, increase fluid to 32 -40oz/hour.
- For temps above 80 degrees: Caloric intake remains the same or decreases depending on GI status, increase sodium to 1200 mg/hour, increase fluid to 40-48 oz/hour.
3. Three bodily systems to monitor:
- Urine output: For the first 4-6 hours, I make sure I pee large amounts (enough to soak my socks if I pee on the bike). If I do not, then I increase my fluid intake. Beyond 6 hours, I make sure I pee in smaller but not small amounts every 2.5 to 3 hours. If I do not, then I increase my fluid intake in small frequent amounts.
- GI: Every 15 minutes (every time I eat/drink), I check to make sure my GI system has good blood supply and is moving/absorbing the fluids and calories I am ingesting. The signs that my GI system is working properly:
- I’m not burping too much
- I’m not vomiting---not even just a little bit of reflux.
- I’m passing flatus
- I don’t have abdominal bloating.
- I’m not nauseous.
- If I have any increased burping, nausea, vomiting (even a tiny bit of acid reflux), bloating, not passing gas: I immediately slow down, sip small amounts of water, cool myself off by pouring water, ice on myself. I don’t take any salt tablets or calories or sports drink until my GI system is working again. Typically, I’ll stop burping, pass some gas which causes my bloated belly to deflate---that’s when I know my gut is working again. At that point, I will slowly increase my effort and slowly take in more water and sodium.
- If my GI system doesn’t start working again despite the above measures or I have vomiting and dizziness/lightheadedness, then I really slow down or completely stop, continue to cool myself, and sip even small amounts of water until the GI system is working again.
- Mental status and general overall well-being: I’m not suggesting that you be overjoyed and ready to solve MENSA puzzles throughout the entire IM race day. However, if you are losing mental focus, having visual changes, feeling dizzy/lightheaded/”out of it”, losing control of your arms and legs, having persistent numbness and tingling, then something is wrong.
By monitoring your intake, urine output, GI status, mental status: you should be able to figure out if you are dehydrated, hyponatremic, have GI shutdown. More importantly you should know what to do about it, address the problem, and go on to have a successful race.
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Comments
Wow! Excellent article. Thanks Kitima!
Very helpful reminder of what we should be monitoring nutrition-wise during training and racing. When I didn't follow this advise I always paid the price.
Amen and Hallelujah!!! Now something that can go in the wiki and we can paste the link over and over and over and over... How many times in the course of a season does this come up? If peeps don't heed, then it's at one's peril. (Insert head bashing smiley here!)
Those of us who know salt works can now just cut and paste! Amazing and awsome job! Profound thanks!
Also, folks, if you need to use sodium dump the Endurolytes, and other products like that with minimum sodium. There's nothing in them. Get something like SCaps or other products that have 300+ mgs of sodium compared to things like Endurolytes that have 40. Unless you enjoy taking handsful of pills during a race.
SCaps also have buffers for the stomach, potassium in useful amounts, and a solid ratio of electrolytes. (I have no affiliation with them--just immense gratitude. Those little capsules have saved many a training day and race.)
Mike
Well done.
Great stuff!!! Thanks for this very valuable training tool Kit!
All, it's already in the wiki and added to the Table of Contents
Thanks for posting, now I need to actually schedule it into the plan.