It is generally well known that replacing fluid lost as sweat is critical for maintaining performance and preventing dehydration. However, drinking too much water or low-sodium beverages during longer exercise sessions and/or in high temperatures can be just as risky, not only to performance, but to your health. It can dilute blood sodium levels and lead to hyponatremia — a dangerous condition, especially in extreme cases.
Your goal should be to stay between your pre-exercise weight and 2% less at all times. For example, if your starting weight was 150, you should stay between 147 and 150. This is your hydration zone. If you gain weight over the course of an exercise session or lose more than 2% of your body weight, your performance and safety can be compromised.
Hyponatremia – the dangers of drinking too much
Hyponatremia is the medical term for low blood sodium. Exertional hyponatremia, is low blood sodium that is believed to occur from consumption of more water before, during and/or after prolonged physical activity, than is lost during the activity. Sodium loss, primarily through sweating, may also be a contributing factor. While milder symptoms include headaches, nausea and cramps, this condition can have tragic consequences. In 2002, two deaths in marathons were attributed to hyponatremia.
Who’s at risk?
Anyone performing prolonged or repeated exercise, for example, triathletes, hikers/backpackers, marathoners, ultra-endurance athletes, adventure athletes and military recruits. Athletes with low sweat rates may be at risk because they may drink more than they lose through sweat. Athletes who are ‘salty’ sweaters may also be at greater risk. A recent study showed that those who finished a marathon with hyponatremia were more likely to be female, have a slower finishing time and have taken an NSAID like naproxen, ibuprofen or aspirin, before or during exercise.
Symptoms of hyponatremia
Symptoms of hyponatremia can be confused with symptoms of dehydration or other heat illnesses, so diagnosis should only be made by a medical professional. Symptoms include: swelling and tightness of the hands and feet, fatigue, weakness, lightheadedness and dizziness, cramps and muscle spasms, nausea, vomiting, headache, confusion and seizures.
Hydration strategies should take into account an individual’s sweat rate as well as climate, intensity and fitness level. By performing a one-hour test workout you can learn how to more closely balance your fluid intake and fluid losses. To access the PowerBar hydration calculator, click here. Ideally, sweat rate should be determined in conditions that closely mimic actual conditions during the workout or competition.
It’s also important to avoid NSAIDs such as naproxen, ibuprofen or aspirin before or during prolonged physical activity. And if you are on prescription medications, ask your doctor if they have an impact on sodium levels.
If during or after activity you begin to have any of the symptoms of hyponatremia listed above, stop and seek medical attention.
What to drink during endurance exercise
Water provides necessary fluid without carbs. Most juices and soft drinks are too concentrated in carbohydrate and can slow hydration. Sports drinks with a 6-8% carbohydrate concentration (14-20 grams of carbs per 8 oz) serving provide needed muscle fuel during exercise without slowing hydration. Drinks that have a lighter taste will help prevent you from wanting to dilute, therefore keeping the carbohydrate concentration in the optimal range. You also want to look for drinks with 500-700 mg of sodium per liter (approx 120-160mg per 8 oz serving). Sports medicine authorities, such as the American College of Sports Medicine (ACSM), recommend sodium and no other electrolyte during endurance exercise. Note: PowerBar Endurance, one of the newest entries into the sports drink category, has 17g of carbs and 150 mg sodium per 8 oz serving as well as lighter taste to help keep you from wanting to dilute. Read on for information on electrolytes.
Electrolytes are minerals that carry an electric charge in your blood and other body fluids. They are involved in many body functions and have important effects on the amount of water in the body, muscle action and the acid-base balance of the blood. The main dietary electrolytes are sodium, chloride, potassium, calcium and magnesium.
Not surprisingly, most Americans need to consume less sodium in their diets and as pointed out in the recently published 2005 Dietary Guidelines, they need to consume more potassium, calcium and magnesium. The story changes as far as sodium is concerned for most athletes. For just about any athlete performing multi-hour workouts, especially in the heat, sodium losses of several grams are not uncommon, with smaller losses of the other electrolytes. Electrolyte concentrations in sweat vary, though. ‘Salty sweaters’ can typically be identified by the white crust on their faces and clothes after a tough workout or race.
What level of electrolyte(s) should be consumed during exercise?
According to current recommendations, sodium is the only electrolyte that should be replaced during exercise. The ACSM, as noted previously, recommend 500-700 mg of sodium per liter of fluid consumed during exercise. This level of sodium may help prevent dangerous drops in blood sodium, while also helping to prevent dehydration-related performance decline. As for the other electrolytes, these are safely replaced through a normal, well-balanced diet.
• Pre-workout, check your hydration status by looking at your urine color. Light colored, like lemonade, is the goal. If it’s dark, like apple juice, drink some more.
• In terms of general guidelines, the American College of Sports Medicine suggests drinking between 6 and 12 oz of fluid every 15-20 minutes during activity.
• However, because of the wide variation in sweating rates (and therefore the general hydration guidelines), occasionally weigh yourself pre and post-workout. If you lost weight, drink more next time (each pound is equivalent to about 16 oz). If you gained weight, drink less. Or check out the hydration calculator, to determine more precisely your own fluid needs..