Endurance and Dehydration

I touched on how tough my long run was during my first peak week. The heat index was 88*-- way too hot for the end of September.

Running in the heat really got me dehydrated, and I started to feel nauseous after the run. I thought I'd drank enough -- two full 16 oz bottles of water and a 20 oz Gatorade as well as two stops at a water fountain. Still, it wasn't enough.

I make a habit of weighing myself right away in the morning and then again after a workout to see how much fluid I should replace. I'd lost around nine pounds. It isn't unusual for me to lose 4 - 5 pounds during a long run in the heat, but considering I'd drank a fair amount, nine was pretty high.

Nine pounds might sound like a lot, but elite marathons much lighter than me have lost more. Haile Gebreselassie is reported to have lost 12.5 pounds (almost 10% of his body weight) during the Dubai Marathon in 2009, and other marathoners have lost similar amounts. You can read more about it in, "How Much Do Champion Marathoners Sweat and Drink" from Runner's World.

Traditional advice has been, "if you wait until you're thirsty to drink, you're already dehydrated." In fact, it's actually more dangerous to drink too much water. Hyponatremia is a condition caused by over consumption of water. Your blood sodium can drop dangerously low, and you could experience symptoms like seizures, confusion, or even death. Read more about it in, "Tim Noakes on the Serious Problem of Overhydration in Endurance Sports."

Which brings me back to my run long run in the heat. Since I first read about hyponatremia, I started drinking more to thirst, but I found like I still wasn't getting quite enough fluid. Now, I drink just a little bit more than I'm thirsty for, and I seem to feel better. During the long run in the heat, I didn't have quite enough water to keep up with my thirst. I retrospect, I should have stopped at the water fountain a few more times.

When I got home I was planning on drinking some chocolate milk to replenish lost fluid, carbs and protein, but I didn't think milk would sit well, so I drank some water and Sprite. Unfortunately, it didn't stay down. For the next hour and a half, I tried really hard to keep from throwing up, but it just kept happening. Fortunately, the Sprite started to go down, and then I could start drinking plain water.

So the next time you're working out, remember that thirst is a pretty good indication of how much you should be drinking.

Run well.