Fluid and Electrolyte Balance for AthletesAug 31, 2012
I learned my lesson this year when it comes to hydration. As I wrote about last month, we did our first long bike tour this summer: The Courage Classic. The first day of the classic this year we started in Leadville, looped around Turquoise lake then rode up to Fremont pass before descending to Copper Mountain resort. The first 15 miles or so around the lake were beautiful and exciting with steep, winding ascents and descents. The next 18 miles up to the pass was a steady climb with a steep finish. I knew as I started the final climb up to the pass that I was feeling slower and slower, and when I finally reached the pass I was ready for a snack. Over the past 3 ½ hours I had drained my large bike water bottle, perhaps 25 oz or so, plus 4 or 5 oz at one of the aid stations.
At the aid station atop Fremont pass, I got off my bike and found a snack--a crustless pre-manufactured white bread pb&j in a plastic wrapper. Under the circumstances, absolutely delicious! I took a couple sips of water then went to chat for a moment with someone from my team. We gave high fives, said good job, I smiled and turned away. As I turned, I noticed that all the muscles in my face had frozen into place. It occurred to me at that moment that perhaps I had not properly prepared with water and electrolytes for the race. I forced my cheeks out of their joker-mask configuration and got back on the bike.
The rest of the day was good, I had a fun screaming fast ride down into Copper Mountain and all was well; but I paid for it with a doozy of a headache for the rest of the day. I also know my performance and fatigue was seriously affected by my dehydration. The next day I doubled the water consumption, rode faster, and wasn’t tired at the end of a similar ride.
So how much water do we need when we exercise? A good rule of thumb is that if we are sweating at a maximal rate, we lose about 1 oz/minute. This means that if you are going full-tilt, you will lose almost 1 liter for every ½ hour of exercise. Most endurance sports will cause a 1.5 liter/hour fluid loss, and in high heat you can lose up to 2.5 L/hour. Water weighs about 2 pounds per liter, so we can assume a loss of 3-5 pounds per hour for endurance sports such as biking, running, soccer, etc.
Research has shown that “sweating beyond 2% of body weight can cause significant impairment of endurance through deficiencies in thermoregulatory and circulatory function.” This means two things: First, when we lose too much water through sweat, the body stops sweating and our body temperature rises too high and can make us more prone to fatigue and cramping and can even become dangerous to health. Secondly, when we lose blood volume, the heart is not able to circulate blood as efficiently so we get less ideal oxygen supply to the muscles and brain which also impairs performance. This means, that for a 150 pound person, 1 hour of exercise without replacing the water lost will result in worse performance. If you are going to be out for several hours, working towards 1 liter/hour would help to keep up with fluid loss enough to meet the body’s needs for an extended event.
So what about performance and electrolyte drinks? In most electrolyte drinks, there are three primary components: water, carbohydrate, and electrolytes. Research has shown that for the first hour of exercise, energy primarily comes from glycogen which is stored in the muscles. After this, as the glycogen is used up, the body will rely more and more upon glucose in the blood. For extended exercise, it is recommended to ingest 1 gram/minute, or 240 calories/hour. Generally, it is better to start this before fatigue sets in so the body has time to absorb the calories.
The primary electrolytes that are lost during exercise are sodium and chloride, so again, for prolonged exercise it is worthwhile to supplement with salt; this can minimize muscle cramping and fatigue. While these are the primary electrolytes in the fluid surrounding the body’s cells, the most common electrolyte found in the cells is potassium. Potassium containing foods such as avocados, bananas, and potatoes can be a good follow up to exercise, and coconut water has a very high amount of potassium and is excellent for hydration.
Sports drinks can be useful before, during, and after a workout to keep blood sugar, water, and electrolytes, but you don’t necessarily have to get too fancy. One study compared plain water, sports drink, coconut water, and a sodium enriched coconut water for rehydration after exercise. The sports drink and sodium enriched coconut water were the most successful at rehydrating people, but the coconut water variety was the best tolerated in terms of volume. Another thing to consider for kids following a big event is good old potato chips and a glass of water--they will get carbohydrates, potassium, and salt from the chips which will help with rehydration and prevent muscle cramping.
Groff, Gropper. Advanced Nutrition and Human Metabolism. 3rd ed. 2000.
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