Multisport: Fluid Dynamics - Without sodium, water can overwhelm your body

Written by: Jim Lehman

As the hot and humid summer months approach, we are reminded of the importance of hydration. Convenience store shelves are stocked with numerous water options and everyone seems to have a water bottle on their desk. Water is the most abundant substance in our bodies and it serves many functions. It is involved in chemical reactions, absorbs and releases heat, and serves as a lubricant. Without water, our bodies cannot function properly. As a result, a fluid loss of even 2% can lead to a decrease in performance. With this in mind, we should all be sure to top off our water bottles at the next stop or grab a fresh one next time through the feed zone. The last minute dashes to the porta-potties seem to prove that we are heeding the warnings about hydration; keep drinking water before and during your event and you will be fine, right?

Well, this may not be entirely true. While you are exercising in the heat, your body attempts to maintain a constant core temperature by increasing the rate at which you sweat. This is a great mechanism for regulating heat, but it also results in a loss of sodium through your sweat. If you are only consuming water during your event, you run the risk of diluting the sodium concentration in your blood, which is referred to as hyponatremia, or water intoxication.

This condition typically occurs in ultra distance events, such as 24-hour races and 100-mile mountain bike races, but it has also been seen in events lasting three to four hours. Other individuals who may be at risk are athletes who are participating in multiple events in one day, such as the masters racer who does the 35+, 45+, and the category 2-3 race on a Sunday afternoon. The idea that it is possible to drink too much water goes against the message that has been reinforced lately, but it is possible. So if you want to succeed in these endurance events or do all three criteriums next Sunday, it is essential that you understand the importance of sodium and the role it plays in your bodily functions.

Sodium is an electrolyte that is necessary for water balance, cellular metabolism and muscular contractions. It draws water through permeable membranes and distributes fluid throughout the body. As you sweat you are losing sodium and thus diminishing your body's ability to move water across these membranes. This will eventually lead to dehydration, even if you are drinking adequate amounts of water. Without sodium, the water you drink will not be able to distributed properly and you will feel bloated, nauseous and unable to perform to the best of your ability. Other symptoms of hyponatremia can include headaches, cramps, extreme fatigue, disorientation and slurred speech. If these symptoms are allowed to progress, they can lead to seizures, coma, brain damage, and even death.

How do you avoid such a situation? One of the best ways to do so is to develop a strategy for your water and salt consumption. Your goal should be replace the same amount of fluid you lost or will lose during exercise. You can estimate your fluid needs by weighing yourself before and after a strenuous workout. This will help you determine your usual sweat rate and allow you to plan a fluid intake schedule for your event. In order to ensure that you make an accurate estimate, be sure to perform this test in conditions similar to those you will experience during your event though. Weigh yourself in the morning after you have gone to bathroom and then again after your workout. It is important to be consistent with your measurements. For every pound lost, you need to consume one pint of fluid. As they say, "A pint's a pound the world round".

On the other hand, if you maintained or gained weight you are probably consumed too much water and you may be experiencing lower blood sodium. You should include sodium-rich foods as part of your recovery process in order reestablish an electrolyte balance. Do this gradually over the course of the next 10-12 hours. During this time your body will also increase urine production in an effort to rid itself of the excess fluids.

For several days prior to your event, you will want to increase your water consumption to minimize the risk of dehydration. In conjunction with this, you should also increase your sodium ingestion by 10-25 grams per day. This increased sodium intake will help prevent the dilution of blood sodium levels that would normally occur with this increased fluid intake.

During the event, your goal should be to ingest approximately one gram of sodium each hour. Most sports drinks only have between 100-200 mg of sodium per serving, so you will need to supplement these with foods that are rich in sodium. Be cautious with salt tablets because it is possible to ingest too much sodium when using them. And as with any nutritional changes, be sure to experiment with these during training before trying them on race day.

The emphasis has been placed on hot, humid conditions where you produce large amounts of sweat, but it is possible to experience water intoxication in colder climates also. Even without sweating excessively, you could consume too much water and thus dilute the sodium in your system. This would essentially have the same effect as the hot, humid example. Remember, hyponatremia deals with the blood concentration of sodium, not the absolute amount.

Some other factors that may complicate this condition are the use of aspirin, ibuprofen, and acetaminophen. Many endurance athletes use these drugs before and during competitions in an effort to prevent or minimize pain, but these medications can be harmful because they interfere with kidney functions and may contribute to hyponatremia. Kidneys regulate water content, so it is essential that your kidneys are working properly under these extreme conditions. It is recommended that you wait until after your event to take these medications.

Please do not let this scare you into drinking too little water during your event. The message is to manage your water your intake so that you are replacing only what you have lost and complementing that with proper sodium intake to maintain cellular function. This will lead to a more enjoyable event and keep you out of the medical tent. You can then spend your post-race time relaxing at the local cantina enjoying a large order of chips and salsa, excellent sources of sodium.

Jim Lehman M.S. is a Coach for Carmichael Training Systems (CTS). CTS has personal coaching packages to fit your goals, your life, and your budget. Please visit CTS at www.trainright.com.