IT'S A SCORCHER OUT THERE!
By Chad Kerksick, PhD | Wednesday, July 28, 2010 8:11:26 AM America/New_York
Have you looked at the nationwide weather recently? High temperatures and high humidity seemingly all across the country and the East Coast has particularly been getting hammered. Whether you are a weekend warrior or an everyday athlete, proper hydration and awareness of dehydration are critical. People from all walks of life suffer from heat exhaustion, heat stroke and even death. A few simple steps are important to keep you from suffering any form of heat illness and this article will guide you along. So grab a cold beverage (we're making improvements already) and we'll get started.
When we exercise, our bodies produce heat and lots of it as a by-product of the work being completed by our muscles. It doesn't matter if you are going for a short jog, a bike ride or even mowing the lawn. Your muscles are working and the work results in heat production. Briefly, this fact holds true no matter the temperature outside, but when the outside temperature and humidity climb to adverse heights, you could consider this as a raising of the ante by good old Mother Nature. Outside of getting sunburned and sporting the freshly cooked lobster look and pending skin cancer that comes along with that, the main danger is getting dehydrated and being at risk for some form of heat injury.
For those who compete in some manner while exercising outside, dehydration can set in rather quickly and once it arrives, studies have shown it's almost impossible to prevent further dehydration without stopping the exercise bout or competition (6). Additionally, many research reviews have shown that losing as little as one percent of your body weight as sweat (two pounds for a two hundred pound person) can alter perception and begin to decrease your performance. The greater the percentage you lose the more your performance is affected. In fact, a two percent loss of water significantly increases heart rate and decreases performance while a four to five percent loss of body weight as sweat is critically dangerous and oftentimes results in some form of immediate emergency care. The average sweat rate is reported to be around 1.7 liters of fluid per hour (3.74 pounds of water) and the highest ever reported was 3.7 liters of water per hour (8).
Tip #1 - Monitoring fluid levels. You can estimate your sweat rate by measuring your body weight (preferably when you're naked) before and after the exercise bout (naked again) (2, 9). For every pound of body weight lost, you need to drink an additional two cups of fluid to replace what was lost. As an example, if an athlete participates in a soccer game for two hours and loses three pounds during the soccer match while consuming 32 fluid ounces (4 cups) of sports drink, this athlete would need to consume an additional 6 cups (48 fl oz.) of fluid to replace what was lost (10). The other simple way is to monitor the color of your urine (2-4). When you are well hydrated, your urine should be clear or a very light yellow and as you become more and more dehydrated, the more yellow, then orange and eventually brown (it's gross and stinks!) your urine becomes. In summary, dehydration is a real threat to your health and performance when exercising outside in the heat.
Tip #2 - Hydrate effectively. An effective approach is to 'prehydrate' meaning drink fluids religiously before the exercise bout and develop a plan to stay hydrated. As mentioned, once dehydration sets in, even the most diligent athlete can't offset its development unless they stop the exercise (6). Sure you could drink enough, but studies have shown your stomach can only release fluid so fast (11-12) so what you are left with is a belly full of water sloshing around while you're running. Recommended guidelines are to drink liberally in the 4-6 hours leading up to the exercise bout (5-6). If it's first thing in the morning you need to start the night before. Approximately one hour before the exercise bout, drink two cups and another two cups 15 - 30 min before beginning (5-6). Once you begin, a regular ingestion plan needs to be utilized and drinking 1.5 - 2 cups every 15 - 20 min is a commonly recommended guideline (5-6).
After the exercise bout, you should weigh yourself to determine how much fluid to drink and after that drink accordingly while monitoring your fluid levels (5-6). When sweating, we lose fluids and electrolytes (key ingredients that help all of our cells function properly) and in addition we are burning away our limited supply of carbohydrates as well. So the ideal drink will replace all three of these things: 1) lost fluid, 2) lost electrolytes, and 3) lost carbohydrate. More specifically, studies have shown that the ideal percentage of carbohydrates should be around 6 - 8% or 6 - 8 grams of carbohydrate for every 100 ml of fluid (6, 8). Less than this doesn't effectively replace lost carbohydrate and you'll begin to run out of fuel faster. More than this is too concentrated and you can actually become more dehydrated as your body attempts to digest it. Sports drinks as we know them are formulated to contain all three of these things and in the ranges of 6 - 8 %.
What are some other popular beverages and how effective are they? Coffee contains fluid but typically doesn't contain much carbohydrate (unless you sweeten with real sugar a good bit) and misses out on electrolytes. It also has some slight dehydrating characteristics which is really the last thing you want to deal with.
Soft drinks or fruit juices contain fluid and carbohydrates and may contain some electrolytes, but the carbohydrate content is too concentrated which will make it difficult for your body to digest, leaving you susceptible to stomach cramps and other gastrointestinal problems. You can try diluting either one of these or taking one drink of water and one drink of the other, but frankly this is a hassle.
Fitness waters have become all the rage and while they do provide fluid and a small amount of electrolytes and carbohydrate, they are not optimal formulations. They don't contain enough carbohydrates (that's how they reduce the calories in them) to replace what you are burning during exercise.
Last but not least is water. Water replaces lost fluid, but doesn't contain electrolytes or carbohydrates. On a side note related to water, it's much more effective to cool your body if it gets inside you as opposed to on your head or anywhere else on your body, so drink it, don't dump it.
Another popular option is carbohydrate gels that come in packets. These are great alternatives, but look at them as a concentrated source of carbohydrates and energy. To optimally digest while exercising you must drink copious amounts of water to provide something for your body to mix with it to break it down. (Another tip, slightly off-subject, is to not try anything new the day of a race, no matter how great it may seem. This goes for a new pair of shorts, shoes, or beverage. You've trained too hard to have the big day ruined by a blister, a chafed private area or stomach cramps.)
Supplementation with glycerol has been shown to help hydration by 'hyperhydrating' or packing additional fluid into our blood and other water-filled compartments (13). When supplementing with glycerol, studies have shown that your body holds on to more water. While a possibility, it's critically important that an athlete develop a comprehensive strategy using the tips outlined above before considering glycerol and this practice is much more important for athletes exercising outside for several hours.
Another effective tip is to increase your intake of foods that contain a significant amount of water, electrolytes and carbohydrates. Fresh, citrus fruits are great for this. Strawberries, raspberries, watermelon, honeydew melon, cantaloupe, pineapple, etc. all contain large amounts of water along with carbohydrate. Also, for those people who are 'salty sweaters' or sweat excessively, liberally salting your foods provides a healthy dose of sodium, an important electrolyte.
Lastly, can you drink too much water? The answer is yes. While dehydration can be dangerous, some people take it too far and drink too much water for how much they are exercising. They have the greatest of intentions, but in their good efforts they end up putting their body at risk for another condition, which is equally dangerous and that is hyponatremia. Hyponatremia is clinically defined as low sodium levels in your blood (1). Sodium is an electrolyte that our body needs in optimal amounts for our cells to work properly. When sodium gets low, your brain function gets altered and you might begin to feel nauseated, disoriented, confused, fatigued, etc. (6-7), all symptoms that sound and feel much like dehydration. The problem is that when people go this route and feel these symptoms they think they are dehydrated and drink more water, which is the last thing they should do. This typically only happens to people who only drink water and as a result are not replacing the sodium they are losing in their sweat. Fortunately, an easy solution is to never drink only water and mix in some form of a sports drink every time you drink something. If you must, lightly sprinkle some salt in your water and this can help.
In summary, exercise outside in the summer is great fun, but the heat can be dangerous without the proper precautions. Follow these steps throughout and you should avoid any major heat-related problems.
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