Science Series 41: Electrolytes and Me

As I approached mile 17 of the 2009 NYC Marathon, my legs began to cramp up. I blamed my lack of training and my dislike of Gatorade. In 2010, I was well trained for the marathon, took in more Gatorade and salt. My legs still cramped. Why is that? Let's break it down (Stop, Hammer time).

Somewhere after mile 18, MP paces me as I fight the pain.

Sources
These are the three primary sources I tapped. Thanks to the original authors and to all that have contributed to these theories I learned about.

health.howstuffworks.com
Active.com
Lore of Running, by Dr. Timothy Noakes

Muscle Cramps
A muscle cramp happens when your muscles involuntarily contract and/or expand when they are not supposed to. You'll generally notice this happening because it hurts like hell. Sometimes you can actually see the muscle spasm under your skin. There are only "theories" about what causes them. That basically means the scientific community isn't satisfied by the method of "proving" the causes. There are lots of anecdotes and little controlled clinical studies using the scientific method- you know, that thing we all learned in middle school chemistry class where some of you burned your hair with Bunsen burners.

The sports related theories are as follows:

Excess use of muscles/lack of conditioning- You work your muscles so much, firing off your neurons, contracting and expanding, to the point of which they are incapable of doing it any longer.

Dehydration/electrolyte depletion- Your body needs water and an appropriate balance of electrolytes to function.

Injury Defense- Something is injured and the muscle around the injury cramps in an attempt to protect it.

My cramps were not caused by injury, and based on the training that I did, I'm not willing to say I was under-conditioned for the race pace I set. So let's focus on the electrolytes.

Hurting. Me and that guy in the foreground too.

Electrolytes
Electrolytes are electrically charged ions that can move to either a positive or negative charge mainly do to the gain or loss of protons in its atomic structure. These electrolytes are important because your body uses these guys to carry electrical impulses throughout your body, including from your brain to your muscles. Cool, huh? So if you are electrolyte depleted, electrical pulses will not be carried properly and your muscles will not contract and/or expand when you ask them to. An individual needs about 8,000mg per day to function normally. Keep that figure in mind.

The main body electrolytes are:
* sodium (Na+)
* potassium (K+)
* chloride (Cl-)
* calcium (Ca2+)
* magnesium (Mg2+)
* bicarbonate (HCO3-)
* phosphate (PO42-)
* sulfate (SO42-)

Sodium and Chloride make up the majority of these electrolytes. They also form table salt (NaCl) when combined. Potassium is another that I will mention. The two primary electrolytes responsible for water content control in and out of cells in the body are sodium and potassium. While sodium generally exists outside the cell, potassium is found inside. Because of this, it is mainly sodium that is lost while sweating. The concentration of electrolytes differs by each individual and is also dependent on acclimation to climate condition. I'll be using average amount and assume the individual is acclimated.

Holding the line... the cramps will not beat me (just slow me down).

Mole to Mg Conversion
Does anyone remember how to do this from high school chemistry class? It's been a while. Sorry Mr. Zentz. I remember that a mole is a mole is a mole, as you used to say, but couldn't remember what the hell that meant. I had to look it up and still I cannot get my math to work out.

A mole (mol, or mmol for one thousandth of a mole ) can be converted to grams by multiplying the average atomic weight of the molecule by the mol amount. But I think other factors, such as ionization are important (ie, counting the extra protons). Rather than trying to teach you and myself this, I will be using the figures given in the Lore of Running book, by Dr. Tim Noakes.

Average electrolyte contents of sweat and blood.

Sweat Rate
So how much do we actually sweat? This is very individual. Again, assuming acclimation, the average runner sweats at lets say 1 liter per hour. Based on this, a runner could lose 1840mg of sodium and 100mg of potassium per hour. If you've never had problems with electrolytes during your runs, then this blog probably isn't really that interesting to you and you probably fit into this average. Alberto Salazar was recorded to sweat at a rate of 3.7 liters per hour. Yikes.

To measure your sweat rate, weigh yourself right before you run. Then run, and weigh yourself right after. One pound lost equals 15.4oz (.455 liters) of sweat. If you drink water during your run, be sure to add that as well.

So the last time I weighed myself before and after a run was in the spring of 2009. I lost 8lbs on a 90 minute run and drank about 12oz of water on my run.

8lbs= 3.64 liters of sweat
12oz of water = .4 liters
That adds up to about 4 liters of sweat in 90 minutes.
And that calculates to a rate of about 2.67 liters per hour.

Yup, I sweat a lot.

Turning on to Park Ave South, tasting the forgiveness.

Absorption Rate
So we should just take in the same amount of water and electrolytes as we lose? No. Definitely not. Ideally you'll take in just enough to get you through the race and you can replenish the rest after. You know, so you stop less and carry less water. But there are other factors to consider, such as absorption rate. Our bodies can only process so much at a time- there is a limit to the amount of water, electrolytes, and calories we can take in per hour.

What is that limit? I'm glad you asked. Again, it is individual. And there are different theories about what the body is capable of. It is thought that combining the right ratios of water, carbohydrates, and electrolytes will will optimize absorption. Check out this theorized ideal combo:

ideal fuel ratios

Sorry I didn't calculate the mg of Carbs from the mmol figure above, but the source didn't give its chemical equation. Studies show that because these different elements are absorbed in different places in the digestive track (ie, water in the stomach) the ratio changes as digestion happens. This actually allows for even higher rates of absorption. Anyone else out there think that's kind of cool? To find your individual rate, all I can offer is trial and error. Just see what you can do, within the scope of what you need to do (ie, don't try to drink a gallon of salt water if you're not showing signs of dehydration and electrolyte depletion).
Now compare the electrolyte content of sweat and the absorption rates and ratios to the electrolyte amounts in popular sports drinks. Since sodium is the primary electrolyte lost, let's focus on it.

electrolyte content

Lacking, huh? I want to give props to Gatorade for even starting this trend of electrolyte replenishment. But they're not going to change their formula if it makes their drink taste bad (or worse than it already does). Above is the figure for their endurance formula. Their normal stuff is much worse. From these figures, one could easily argue the content should be at least twice what it is. So I take salt, as I'm sure many of you do. And I drink V8 regularly during the week and for recovery- criticized for high sodium content, this is quite ideal for runners, as is the tons of potassium and other goodies.

Aldosterone: Less is more?
How one should preemptively take in electrolytes is debated. Your body regulates your electrolyte balance with something called aldosterone. If you need electrolytes, aldosterone will up the amount in your body. If you have too much, it will turn off. So eating salty foods encourages the aldosterone to stop doing its job. And you are potentially acting against your own natural physiology. But when exercising, you lose more electrolytes than your body can manage.

How do we reconcile this? Again, I'm not finding a definitive answer. My advice would be that if you take in electrolytes early, you should continue to do so throughout your run and after, restoring your levels "manually" while your aldosterone kicks back in. And at the appropriate ratios too.

Victory. But I know I have an even better time in me.

Mistakes and Lessons

So here's the math of my 2010 NYC Marathon. At a sweat rate of 2.67 liters per hour, I was losing 4,913mg of sodium per hour. I was taking in about 300mg of sodium per hour via Gatorade & Gu up until I took in 1,500mg of salt (perhaps 2/3 of which is sodium versus 1/3 of which is chloride) at mile 15. I reached mile 16 in about 2 hours and that's when the cramps started.

Me by mile 16:
9,826mg of sodium lost
1,600mg of sodium gained
That equates to approx 8,200mg net sodium lost
Remember the amount needed daily for normal body function? About 8,000mg.
Oops.

The average sweaty person would have lost about 4,000mg of sodium netting a loss of 2400mg. Manageable. I should have taken in more sodium and sooner. There's still a concern that my absorption rate may not be able to handle it- my feet may be too fast for my digestion. Kind of funny. But only kind of. I 'll have to test this. But even if I was average and took in 2,800mg of sodium per liter of water per hour, I should be perfectly fine in the marathon distance.

Something else... Coconut water, loaded with potassium but little sodium, isn't the ultimate electrolyte gift from God I thought it was. I thought sodium and potassium were interchangeable, but as you and I now know, they are not. I drank a lot of it thinking I was prepping appropriately. For electrolytes lost via sweat, salt rules.

And my final lesson... I am a really big running geek. Oh wait.... I already knew that.

So now I take a break, letting my calf heal properly from the injury that was probably caused by cramping 2 weeks before the NYC Marathon. Hopefully by late December I will be able to apply some of these theories, and by May put all this science to the test. Look out Fargo 2011. Here I come.