DRINKING IT IN
Coping with training and racing in the heat
There's a good chance that the summer season will find you racing and training under the most physiologically severe conditions that can be imposed upon your body: heat and humidity. Heat limits your ability to train. When you exercise, your muscles rely on a sufficient blood supply to bring them oxygen and fuel. But blood must also go to your skin's surface to dissipate heat and cool your body. Sooner or later, the heat produced can become so great that your muscles no longer receive the blood they need to continue exercising, while your skin is denied enough flow to cool you properly.
Sweating is your body's primary mechanism for shedding excess heat and maintaining an appropriate core temperature. To cool you effectively, sweat must evaporate rather than simply drip off your skin. However, when humidity is high, the air is already saturated with water, and less of your sweat evaporates. Your risk of developing dehydration and even heat illness increases greatly when you train in these conditions.
Fluids lost from sweat must be replaced to prevent dehydration. An average size cyclist can sweat 2 or even 3 quarts of fluid per hour while training in the heat. When you figure that water weighs nearly 8 pounds per gallon, and losing as little as 2 percent of your body weight can impair your training efforts, it's clear that cyclists need to practice effective strategies for coping with training and racing in the heat.
How quickly you adapt to exercising in the heat is highly individual, but full adaptation can take one to two weeks. When you train in hot weather, your body uses more muscle glycogen, which can result in fatigue sooner than in cooler weather. Even when you do become acclimatized, you will not perform at your best, though acclimatization can slow down this increased glycogen use.
Acclimatization increases your blood volume and improves transfer of heat from deep body tissues to your outer shell. Sweating starts sooner during exercise, and after 10 days of training in the heat your sweat capacity is nearly doubled. Sweat also becomes more diluted in an attempt to preserve the body's electrolyte balance.
While sweating is crucial to cooling your body, the fluid lost during training must be replaced for exercise to continue, especially when you are sweating more heavily. When you don't replace fluids adequately, your blood volume decreases and your heart rate increases. And since even the best drinkers are only able to replace about 80 percent or less of their fluid losses, "catch-up" drinking is not an effective hydration strategy.
It is important that you hydrate before exercise. To prepare for the next day's training, consume 16 ounces of fluid before bedtime. In the early morning, consume 16 to 24 ounces of caffeine-free fluid. Fluids containing caffeine are thought to be worth half of their actual volume (8 ounces of coffee equals 4 ounces of fluid). Before training, you should consume 8 to 10 ounces of fluid every hour. Then you can start to hyperhydrate one hour before exercise by consuming 16 to 32 ounces of fluid. Twenty minutes before training, drink an additional 8 to 16 ounces of fluid.
In the hour before exercise, a sports drink may be your best fluid choice. These drinks provide carbohydrate and sodium and offer some hydration advantages over plain water. You can also start a race or training session with a fluid-swollen stomach, if you're comfortable with the feeling. Fluid leaves your stomach faster and enters your bloodstream sooner when your stomach is stretched. Experiment to see what volumes do not exceed your comfort level.
While training, strive to consume 4 to 8 ounces of fluid every 15 to 20 minutes. Set your watch as a reminder to drink at specific intervals. Take big gulps, so fluids empty more quickly from your stomach. Start your drinking on the bike right away. If you become dehydrated, your stomach empties more slowly, making rehydration difficult.
If your training session or race is longer than 90 minutes, or lasts 60 minutes at high intensity, your best fluid choice is a sports drink. The carbohydrate in the drink offsets muscle glycogen losses and maintains blood glucose levels. These drinks are especially important in hot weather when muscle glycogen depletion can occur more quickly.
Sports drinks also provide sodium, an important electrolyte lost in sweat. When you go out for very long training rides or compete in races lasting several hours, you may be at risk for developing hyponatremia, low blood sodium levels, which can have dangerous consequences.
Hyponatremia is more commonly seen in ultraendurance exercise, such as an Ironman triathlon, and among slower marathon finishers. Sodium concentration in the blood can decrease when you lose large amounts of salt from sweating and use only plain water to replace lost fluids. Essentially, you dilute the sodium concentration in your blood.
To prepare for these sodium losses, you can increase your intake of salty foods or salt the day or two before a long ride or race (unless your doctor says otherwise). Avoid drinking plain water during exercise when a sports drink or a gel containing sodium is available. The sodium found in sports drinks also improves their taste, enhances fluid and glucose absorption hrough the small intestine, and can encourage thirst and drinking. If plain water tastes better in the heat, consider one of the sports drinks on the market that has little or no flavor.
Rehydration and refueling are top priorities after exercising in the heat. You want to fully restore fluid losses from one training session to the next. And bear in mind that thirst is not a reliable indicator of fluid loss. If you are thirsty, you are already dehydrated. The thirst mechanism also shuts down before you have sufficiently replaced all your fluid losses.
Weigh yourself before and after training. Try to consume 24 ounces of fluid for every pound of weight lost to replace both sweat and subsequent urine losses. Sweet or slightly salty products may stimulate your desire to drink. Cool drinks are usually more palatable.
Sodium or salt may not only stimulate your drive to drink, but can also enhance the rehydration process. Sweating results in large fluid losses and relatively small sodium losses (unless conditions are extreme). After training, your blood volume and total body water is reduced, while there is a mild increase in blood concentration. Consuming large amounts of plain water after exercise can dilute your blood before your full blood volume has been restored. This dilutional effect shuts down the thirst mechanism and you urinate to bring your blood concentration back to normal. The end result is that you will produce a large amount of diluted urine before you are fully rehydrated.
A series of studies determined that rehydrating with drinks higher in sodium produced significantly lower urine losses than low sodium drinks, indicating that more of the fluid consumed was retained. You can include sodium in your recovery drinks, and continue to emphasize salty foods after exercise to rehydrate properly. It is also recommended that you consume 50 to 75 gm of carbohydrate after exercise, in addition to fluid and sodium for optimal recovery.
Monique Ryan, RD is a sports nutritionist in Evanston, IL. She is the author of Complete Guide to Sports Nutrition.
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| Title |
Drinking it in: coping with training and racing in the heat. |
| Source |
VeloNews |
| Publisher |
Inside Communications, Inc |
| Vol (iss) |
31(9) |
| Date |
3 June 2002 |
| Pages |
40-41 |
| SIRC ID # |
S-830538 |
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