Training

NANCY CLARK: Sweat, Cramps, Fatigue

The Athlete’s Kitchen

Copyright: Nancy Clark MS RD CSSD April 2013
 
Sodium, Muscle Cramps and Sweat Losses: Tips for Sweaty Runners
 

We’ve all heard the 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 endurance runner 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.

      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 hyponatremia dropped.

The information in Waterlogged challenges the theory drink before you get thirsty. Noakes believes elite athletes who become champions can tolerate significant sweat loss without intolerable thirst. He contends the associated weight lost via sweating enhances performance. Others question if those athletes could run better if 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 runners feel thirsty at about 2% dehydration. At that point, they'll start looking for water. Ultrarunners can maintain performance at 3% 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% dehydration equates to a 3-pound sweat loss for a 150-lb. runner.)

• 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 runners 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 runners drink excessively during prolonged exercise. It can also occur when even dehydrated endurance athletes lose significant amounts of sodium in sweat. Data from 669 ultramarathoners indicates 15% experienced low blood sodium. Of those, 24% were overhydrated, 36% 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 runners are salty sweaters. Runners accustomed to exercising in the heat retain more sodium than unacclimatized runners. (Compare the saltiness of your sweat on first hot day of spring vs. in the fall.)

• Athletes lose relatively more 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 ultramarathon, blood sodium can be low even in a dehydrated runner. 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 over-drinking. The 220 milligrams of sodium in 16 ounces of Gatorade is far less than ~1000 milligrams of sodium in 16 ounces of sweat loss.

• Noakes says evidence is lacking to prove that runners 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 were the problem, wouldn't the entire body cramp, not just one muscle?

• Exercise-induced muscle cramps occur in muscles that perform repetitive contractions. Runners 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.)

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

• A runner 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; the runner collapses. What to do? 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 runner 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 “real” foods (salty pretzels, pickles, chicken broth, ham-cheese-mustard wrap) during ultraendurance events can do a fine job of providing needed electrolytes. Just don’t get too aggressive with water or sodium intake—and have fun!

 

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 and marathoners offer additional information. They are available at www.nancyclarkrd.com. See also sportsnutritionworkshop.com.

 
 
Reference:
(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.