Sweat: Sodium, Muscle Cramps and Fluid Loss

By Nancy Clark MS RD CSSD

You’ve probably heard stories about marathoners and soldiers who have died due to consuming too much water. Clearly, overhydration can be as dangerous to your health as underhydration. So what does a sweaty athlete need to know about staying adequately hydrated without stomach sloshing? Dr. Timothy Noakes’ book, “Waterlogged: The Serious Problem of Overhydration in Endurance Sports,” is an interesting yet controversial resource that addresses that question.

Determining the Right Amount of
Fluid Replacement When Exercising

According to Dr. Noakes, the sports drink industry has effectively marketed a positive image (successful athletes) despite having an overhyped product (salted sugar-water). Noakes believes the sports drink industry has brainwashed athletes to overhydrate – and this has created life-threatening problems. For example, between 1983 and 1998, more than 700 cases of exercise-induced hyponatremia – overhydration that leads to low blood sodium, brain swelling, coma, and even death – were documented in the Gatorade-sponsored Ironman Hawaii Triathlon. The participants had been encouraged to drink copiously. Did that advice backfire? For the Comrades Marathon, participants were told to drink according to thirst. Race organizers placed aid stations every 5 km (3 miles) – and cases of hyponatermia dropped.

The information in “Waterlogged” challenges the theory of drink before you get thirsty. Noakes believes elite athletes who become champions can tolerate significant sweat loss without untolerable thirst. He contends the associated weight lost via sweating enhances performance. Others question if those athletes could run better if they better hydrated.

Below are a few droplets of less-controversial hydration information to help you quench your thirst, perform well, and stay out of the medical tent when you are doing extended exercise in hot weather:

• Our bodies can deal with transient underhydration that lasts from 4 to 8 hours. In contrast, chronic dehydration leads to health issues, such as happens when elderly people are trapped in hot apartments during a heat wave.

• Most athletes feel thirsty at about 2 percent dehydration. At that point, they’ll start looking for water. Ultrarunners can maintain performance at 3 percent dehydration. To determine your percent dehydration, weigh yourself naked before and after your workout. A one-pound drop equates to a loss of 16-ounces of sweat; 2 percent dehydration equates to a 3 pound sweat loss for a 150-lb. person.

• Thirst is a powerful fluid regulator. Noakes disapproves of the advice to drink before you are thirsty because that can create problems with overhydration. Yet, others contend drinking on a schedule can help endurance athletes maintain proper hydration, as long as they do not aggressively overhydrate but rather replace fluids according to their sweat losses (as learned during training via pre-post exercise weigh-ins).

• Exercise-induced hyponatremia (low blood sodium) occurs when athletes drink excessively during prolonged exercise. It can also occur when even dehydrated endurance athletes lose significant amounts of sodium in sweat. Data from 669 ultra-marathoners showed that 15 percent experienced low blood sodium. Of those, 24 percent were overhydrated, 36 percent were dehydrated, and the rest were in fluid balance (but not sodium balance) (1).

• The amount of sodium lost in sweat varies from person to person. Some people are salty sweaters. Athletes accustomed to exercising in the heat retain more sodium than unacclimatized athletes. (Compare the saltiness of your sweat on first hot day of spring versus in the fall.)

• Athletes lose relatively higher amounts of water than sodium. So, under standard conditions, the blood sodium level can actually increase during exercise, unless you overhydrate. But with abnormally high sodium high losses, such as during an ultra-marathon, blood sodium can be low even in a dehydrated athlete. Hence, sodium replacement can be a wise idea.

• The amount of sodium in a sports drink is small and unable to counter the dilution of body fluids that occurs with overhydrating. The 220 mg of sodium in 16 ounces of Gatorade is far less than ~1000 mg sodium in 16 ounces of sweat loss.

• Noakes says evidence is lacking to prove that athletes who cramp have low serum sodium or are more dehydrated than non-crampers. He suggests muscle cramps are related to fatigue, not sodium deficiency. If sodium deficiency was the problem, wouldn’t the entire body cramp, not just one muscle?

• Exercise-induced muscle cramps occur in muscles that perform repetitive contractions. Athletes who get cramps tend to be those who do high intensity exercise, as well as those who have a history of cramping. Note: Many exercise scientists believe there are two types of muscle cramps: some related to fatigue, others related to sodium imbalance. The science of cramping lacks a clear consensus.

• Stopping exercise to stretch resolves muscles cramping. Stretching also resolves nocturnal cramps.

• Drinking about 2.5-oz of salty pickle juice has been shown to alleviate muscle cramping within 90 seconds. This rapid benefit is unlikely due to changes in blood sodium levels. Too quick. Noakes speculates that drinking the acidic pickle juice triggers a reflex in the throat that lessens or stops the cramps.

• An athlete who collapses after the finish line is most likely experiencing blood pressure changes – not severe dehydration. When exercise stops, the heart stops pumping enough blood to the brain and the athlete collapses. Noakes advises to quickly raise the athlete’s feet and pelvis above the level of their heart. This aids the return of blood to the heart and rapidly corrects the situation – without any IV fluids.

So what’s a sweaty endurance athlete supposed to do during prolonged exercise? Learn your sweat rate and drink accordingly. If fluid in your stomach starts “sloshing,” stop drinking! The body can absorb about 600 to 1,000 ml/hour (women/ men). Adding carbohydrates and sodium to the water enhances fluid absorption as well as palatability and performance. Consuming food like salty pretzels, pickles, chicken broth, ham-cheese-mustard wrap during ultra-endurance events can do a fine job of providing needed electrolytes. Just don’t get too aggressive with water or sodium intake – and have fun!

1. Hoffman M, Hew-Butler T, and Stuempfle K. Exercise-Associated Hyponatremia and Hydration Status in 161-km Ultramarathoners. Med. Sci. Sports Exerc. 45(4):784–791, 2013.

Nancy Clark, MS, RD, CSSD (Board Certified Specialist in Sports Dietetics) counsels both casual and competitive athletes at her office in Newton, MA (617-795-1875). Her “Sports Nutrition Guidebook” and food guides for new runners, marathoners, and soccer players offer additional information. They are available at http://www.nancyclarkrd.com. See also her website, sportsnutritionworkshop.com.

The articles written by guest contributors are the sole responsibility of the individual writers in terms of factual accuracy and opinion and do not necessarily reflect the views of the publisher of this blog.

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