All fitness participants want to get the most out of their workouts. But how do your clients and colleagues know if they are getting the right amounts of fluid and
nutrients to fuel their exercise sessions? Is there such a thing as getting too much water when rehydrating? When is it necessary to replenish electrolytes with a sports drink rather than rely solely on water? Do experts recommend restoring glycogen stores after exercise with a protein recovery drink or a carbohydrate-protein mix? Should you eat low or high glycemic index foods to enhance your training performance?
These questions were among the topics covered at the 2003 Gatorade Sports Science Institute (GSSI) Scientific Conference held in Chicago in July.
The Dangers of Hyponatremia
Proper hydration and sufficient electrolyte intake continue to be important concerns for health professionals who work with athletes and active people at all levels and ages. As health and fitness professionals, we usually remember to tell our clients to do these three essential things:
- Take in enough fluids all day to maintain proper hydration.
- Drink extra liquids before and during exercise to decrease the risk of heat-
related illness and to maintain optimum performance.
- Replace fluids lost during exercise.
But there’s more to the hydration equation than that, warns Robert Murray, PhD, an exercise physiologist who specializes in the physiological and performance effects of fluid and carbohydrate intake during exercise. Murray, who also serves as director of the GSSI in Barrington, Illinois, advised attendees to be on the lookout for the signs of hyponatremia. A dangerous condition, hyponatremia can occur when exercisers take in too much water, causing an imbalance in fluid-electrolyte levels. This, in turn, can lead to an abnormally low plasma sodium concentration, which can be life threatening. In the worst-case scenario, Murray warned, sustained
hyponatremia results in a rapid influx of water into the brain and causes swelling
of the brain, possibly leading to seizure, coma and even death.
The faster blood sodium levels drop, the greater the potential problems, noted Murray. Hyponatremia is defined as having a plasma sodium concentration lower than 135 millimoles per liter (mmol/L); the normal range is 136-142 mmol/L. When blood sodium levels decrease to 125 to 135 mmol/L, gastrointestinal distress can result, manifesting in symptoms like bloating and nausea. When levels drop below 125 mmol/L, more serious symptoms develop, including confusion, wheezing, a throbbing headache, swollen extremities, lack of coordination and fatigue. The most severe problems typically occur when blood sodium levels fall below 120 mmol/L.
Overdrinking is especially problematic when athletes ingest large amounts of water without taking in adequate sodium. The condition is also likely to occur when athletes drink large amounts of water in a short time to increase urination or move illegal substances through the system quickly in hopes of “passing” a drug test. In some cases, athletes simply go overboard with fluid consumption in a misguided attempt to prehydrate for an athletic event, or they overhydrate during a long endurance event, such as a marathon. Murray cited one instance of what he called “starting-line hyponatremia,” in which a female marathon runner consumed 10 liters (that’s 17 twenty-fluid- ounce bottles!) of water the night before a race, resulting in severe hyponatremia.
Although hyponatremia is usually caused by excessive drinking, that is not always the case. “This is true most of the time, but not always,” said Murray. The risk of hyponatremia is greater during exercise than at rest. One reason for this is that the body produces less urine during exercise, and because of sodium losses in sweat, the body’s sodium content can become too diluted.
He noted that the following can also contribute to exercise-related hyponatremia:
- heat exposure
- inadequate sodium intake due to a low-sodium diet
- inadequate sodium intake while exercising
- large sodium losses due to excessive perspiration (sweat rates vary greatly from person to person)
- a high concentration of sodium in the sweat (actually visible as white salt encrusted on workout clothes)
- a poor fitness level or poor acclimatization to exercise
Interestingly, women appear to be at a higher risk for hyponatremia than men. Murray hypothesized that this may be because women tend to pay more attention to prehydrating before workouts than male exercisers and are, thus, more likely to go overboard. Women also have slower sweat rates, which could lead to faster overhydration. In making this point, Murray cited evidence gleaned during the San Diego Rock & Roll Marathons in 1998 and 1999, when a total of 26 runners were treated for hyponatremia; of those, 23 were females.
What to Do: Murray offered the following practical suggestions for preventing hyponatremia:
- Athletes at risk for hyponatremia (i.e., those who are heavy or salty sweaters or have suffered from the condition in the past) should be sure to get sufficient salt in their diet by consuming foods high in sodium.
- If a health concern (such as hypertension) requires adhering to a low-salt diet, clients should understand that in order to maintain a proper blood-sodium balance, they still need to replace the salt they lose during exercise.
- During athletic events or intense exercise sessions, particularly those lasting more than 45 minutes, clients should ingest sodium, either by consuming a sports drink or by eating salty foods.
- Athletes should know their personal sweat rates and should replenish lost liquids accordingly during workouts.
- Prehydration should be limited to reasonable and necessary amounts of fluid (i.e., 20 fluid ounces 1 to 2 hours before exercise, and an additional 8 fluid ounces 15 to 30 minutes before the workout).
- Clients need to be reminded not to go overboard with their after-race drinking. When endurance athletes try too hard to replenish lost fluids with plain water, they often subject themselves to the risks of hyponatremia.
Cramps During Exercise
The role of fluid and sodium in preventing heat cramps during exercise was explained by E. Randy Eichner, MD, professor of medicine at the University of Oklahoma Health Sciences Center in Oklahoma City and internist for the university’s varsity teams.
“Heat cramps come from salty sweating,” he said. According to Eichner, heat cramps are usually caused by a combination of these three factors:
- loss of salt
- loss of water
- muscle fatigue
Eichner cited the findings of a recent study on heat cramps involving 10 members of the university’s football team. Players prone to heat cramping had saltier sweat and lost more sodium than players who were “noncrampers.” In one day involving two practice sessions, the “crampers” lost an average of 11 grams (g) of sodium while
exercising compared to the noncrampers’ average of 5 g.
What to Do: To reduce the likelihood of heat cramps, Eichner said, health professionals should encourage athletes to consume salty foods and beverages, such as canned soups, tomato or vegetable juices, baked beans, pickles, pretzels and pizza. Trainers should ensure that during exercise, their clients drink sufficient amounts of fluid containing sodium.
Refueling After Exercise
Although many exercisers watch what they eat and drink before and during an exercise bout, they are often unaware of the importance of what they consume after a workout.
Postexercise refueling was the topic of a session conducted by Edward Coyle, PhD, professor in the department of kinesiology and health education at the University of Texas at Austin. “It’s difficult to train hard at the specific intensity required for competition when not fully recovered,” said Coyle. In fact, the harder and longer an athlete trains, the more crucial recovery fuel becomes. Coyle reminded his audience that during exercise, an athlete loses a combination of fluids, electrolytes, carbohydrate and fat (see “Typical Losses During Exercise”).
Rehydrating. The first task after a workout is to restore the body’s fluid and electrolyte balance by drinking an adequate volume of fluid, said Coyle. Because a significant portion of what an athlete drinks after exercise is excreted as urine, it’s important to rehydrate with more fluid than was lost during the training session.
Coyle estimated that an athlete’s body retains only about half to three-quarters of any fluid consumed after exercise; the amount retained depends on the type of beverage ingested. For example, 50 to 60 percent is retained from caffeinated diet colas; 60 to 70 percent from water; and 65 to 75 percent from sports drinks. In studies he has conducted, Coyle has determined that more fluid is retained in the body when carbohydrate and electrolytes are included in the fluid hydration drink, thus enhancing rehydration. For that reason, Coyle noted, a sports drink may be preferable to other types of liquid after exercise.
What to Do: To rehydrate properly, athletes who have trained for 45 minutes or longer should drink 1.5 times the volume of fluid lost (this is less crucial for those who have exercised at moderate intensities for shorter durations). However, Coyle said the only way to truly monitor fluid loss during intense physical activity is to weigh clients before and after their workouts. The weight loss converted into fluid ounces and then multiplied by 1.5 is the total fluid needed to rehydrate properly and enhance recovery (see “Sizing up Sweat”).
But fitness professionals need to be careful about suggesting this approach, since being weighed can be a sensitive issue for certain clients, especially those who are already overly concerned with their weight. Fitness professionals need to ensure that weighing clients to determine their rehydration needs doesn’t exacerbate any existing weight preoccupations or further contribute to negative body image.
Replacing Nutrients. In addition to losing fluid and electrolytes during exercise, athletes lose carbohydrates in the form of glycogen used by the muscles and the liver. Fats mobilized as energy from intramuscular and adipose-tissue triglycerides are also depleted during exercise. For a look at how much of each of these nutrients is lost, see “Typical Losses During Exercise.”
Some athletes (and even some fitness professionals!) mistakenly believe that muscle glycogen can be quickly restored by eating a high-carbohydrate meal right after a workout. However, Coyle took exception to this, noting that it takes at least 24 hours to recover glycogen stores after intense, extended exercise: “It’s not rapid repletion.”
What to Do: Many exercisers are confused as to which drinks and foods are best for posttraining nutrient replenishment. According to Coyle and other experts, replacing carbohydrate stores immediately after exercise is essential for replenishing glycogen lost from the muscles and liver. That’s because carbohydrates are the body’s prime energy source for exercise.
Coyle also noted, however, that some studies have found that a mix of carbohydrate and protein can be more effective than carbs alone in restoring glycogen levels after exercise. “If you add a small amount of protein to carbohydrate, there may be slightly greater synthesis at particular times,” Coyle said. That’s why he
advises clients to consume 50 to 100 g of carbohydrate along with 10 to 20 g of protein immediately after a workout and to repeat that same combination at 2-hour intervals until the next big meal. Some clients find liquids easier to tolerate than solid foods after an intense workout; a carb-protein recovery drink is recommended for these clients.
The Role of the Glycemic
Index in Recovery
Coyle also shared the results of an interesting study he had recently completed that examined the role of the glycemic index (GI) in selecting effective recovery foods. Simply put, the GI is a ranking of different foods based on their immediate effects on blood sugar levels; the lower a food’s GI, the slower an individual’s blood glucose response is to that food. (For more information on the GI, see “Understanding the Glycemic Index” in the October 2003 issue of IDEA Health & Fitness Source.)
Although the research to date is inconclusive, some experts think that consuming more low-GI foods before exercise may provide a sustained energy source during the workout. Conversely, eating more high-GI foods postexercise may hasten recovery because these foods can be broken down to blood sugar more quickly.
In his study, Coyle compared the effects of eating corn flakes (high-GI) with those of eating bran cereal (low-GI) and found that the rate at which these cereals entered the bloodstream after an exercise session was identical. However, he also found that the low-GI bran cereal actually facilitated glycogen storage more quickly than the corn flakes. This was owing to an enhanced insulin response, which Coyle attributed in part to the higher protein content of the bran cereal.
However, Coyle said with athletes, it’s not just a question of how fast carbohydrates are converted to sugar in the blood; equally important is the rate at which sugar gets back into the muscle to facilitate recovery. “We can’t make simple statements based on the GI [values] of foods,” he warned.
Coyle noted that athletes need to eat a certain amount of fat to recover muscle glycogen levels after workouts. He recommended consuming 20 to 30 percent of calories from fat, which will help “bring the body back to where it should be to restore intramuscular triglycerides.” He went on to say that athletes should try to eat more “healthy” fats, such as nuts, nut butters, seeds, fatty fish (e.g., salmon and sardines) and olive oil.
Finally, Coyle made it clear that many athletes still have a long way to go to maximize their recovery from exercise. When advising these clients, he said, the focus should be on getting adequate fluids and sodium and taking in plenty of carbohydrates with moderate protein and healthy fats to aid in recovery. Coyle’s bottom line: “If we can’t do the basics first, we shouldn’t even think about the other things, such
What to Do: Although individual needs may vary based on body weight and specific activity, Coyle recommends the following for athletes trying to maximize recovery after extended exercise:
- Within 15 minutes of completing a workout, eat 50 to 100 g of “rapidly
absorbed” carbohydrate augmented by 10 to 20 g of protein.
- Continue eating 50 to 100 g of carbohydrate plus 10 to 20 g of protein every
2 hours until the next complete meal.
- Eat 400 to 800 g of carbohydrate daily, depending on the intensity and volume of training.
The Finish Line
Judging by the findings presented, it’s clear that the body of research on sports nutrition continues to evolve, with new discoveries unearthed every day. In the meantime, clients wanting to enhance their athletic performance are best advised to stay well, but not excessively, hydrated;
replace fluids and electrolytes (especially sodium) lost in sweat; and eat well before and after workouts. By adhering to these well-documented principles, your athletes will be the ultimate winners!
To properly rehydrate after exercise, it’s important for athletes to know their sweat rates. These rates can vary based on the individual, the weather and the exercise intensity, so athletes should use the following equation:
- Measure weight prior to the workout (e.g., 120 pounds) and again immediately following (e.g., 117 pounds).
- Subtract the weight lost during the workout (e.g., 3 pounds) and convert that amount to fluid ounces (e.g., 1 pound = 16 fluid ounces, so a 3-pound weight loss would = 48 fluid ounces).
- Multiply this amount by 1.5 to arrive at the amount of liquid needed to replace the sweat loss (e.g., 72 fluid ounces).
To recover properly, clients need to consume this amount within 24 hours of exercise or before the next training session, whichever comes first.
According to Edward Coyle, PhD, an athlete weighing 130 to 160 pounds (59 to 72 kilograms) typically loses the following amounts of liquid and nutrients during a 2-hour training session:
water: 2,000 grams (g)
sodium chloride: 5 g
muscle glycogen: 200 g
liver glycogen: 50 g
intramuscular triglycerides: 50 g
adipose-tissue triglycerides: 50 g
For more information on the GSSI presenters, their sessions or next year’s conference, visit the GSSI Web site at www.gssiweb.com.
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