My client Jack was on a fast cross-country tour: 2750 miles in just 20 days. Seven days into the tour he started riding poorly although he had plenty of training miles in his legs. His buddies noticed he wasn’t urinating at the rest stops and said he was getting dehydrated. Even though he wasn’t thirsty they told him to drink more. After the ride he still wasn’t going to the bathroom so at dinner they reminded him to drink.
The next day he kept drinking but still didn’t start to urinate. By that evening he had a headache and at dinner his friends noticed he seemed confused. His condition didn’t improve overnight so the tour staff took him to the emergency room. A simple blood test revealed he had a dangerously low sodium concentration in his blood, a condition called hyponatremia. The ER doc started an intravenous fluid with a high concentration of sodium.
Jack had developed dilutional hyponatremia from drinking so much fluid that he diluted the sodium concentration of his blood to a dangerously low level. The dilutional hyponatremia had progressed to Exercise Associated Hyponatremia (EAH) and his body had started retaining fluid, rather than urinating it out. Because he was retaining fluid his body started to bloat. His brain tried to swell but couldn’t because it was encased in his skull. This caused the headache.
“Sodium plays a key role in your body. It helps maintain normal blood pressure, supports the work of your nerves and muscles, and regulates your body’s fluid balance. … Older adults may have more contributing factors for hyponatremia, including age-related changes, taking certain medications and a greater likelihood of developing a chronic disease that alters the body’s sodium balance.” [Mayo Clinic emphasis added]
Drinking too much fluid may cause a hormonal change so that your body retains fluid rather than urinating the excess fluid to restore the sodium-fluid balance. Retaining fluid leads to generalized bloating, your skin becomes puffy and your limbs swell up.
According to the American College of Sports Medicine (ACSM), hyponatremia in events under four hours is usually the result of drinking too much before, during and after the event. In longer events, even if you drink appropriately, you may lose enough sodium to develop hyponatremia, so sodium supplementation is a good idea starting early in the event. [American College of Sports Medicine. (2007). Exercise and fluid replacement position stand. Medicine and Science in Sports & Exercise, 39, 377–390.]
“Severe and potentially life-threatening hyponatremia can occur during exercise, particularly in athletes who participate in endurance events such as marathons (42.2 km), triathlons (3.8 km of swim, 180 km of cycling, and 42.2 km of running), and ultradistance (100 km) races. In fact, hyponatremia has been stated to be one of the most common medical complications of long-distance racing and is an important cause of race-related fatalities.” (Exercise Associated Hyponatremia (EAH) in the Clinical Journal of the American Society of Nephrology.)
Elite athletes rarely develop EAH — they’re racing too fast to do more than sip water as they race past aid stations. Most of the cases are middle of the field and slower participants who — worried about dehydration — believe they should drink before they’re thirsty. Some even have plans about how much to drink at each aid station irrespective of how much they’re sweating.
Danger signs. If your urine is dark in color, you may be getting dehydrated, although your urine also turns yellow when you excrete supplements that your body doesn’t need. If you stop urinating, then you may be developing dehydration or your body may be retaining fluid.
To check for dehydration, pinch a fold of skin on the back of your hand or your arm. Let go. If your skin fold almost instantaneously returns to normal you aren’t getting dehydrated. If it takes a few seconds for your skin to return to normal then you may be getting dehydrated. Moderate dehydration won’t affect your performance as I explain in this column Hydrating like the Pros.
Bloating and the resulting weight gain are the most obvious symptoms that you’re retaining fluid. If you start to get puffy around a ring on a finger, or at your glove and sock lines, you are developing hyponatremia. In serious cases, your limbs may swell so that you look like the Michelin man.
If you start to get puffy or gain weight, stop drinking until you urinate freely and the puffiness or extra weight disappears. If you develop puffiness and become mentally confused, your brain is swelling and it is a medical emergency. Call 911 or your local emergency number.
Drink to satisfy thirst
“Drinking according to thirst and avoiding weight gain during exercise remain the most reliable strategy against developing exercise-associated hyponatremia.” [Hew-Butler, Tamara, et al. (2008). Practical management of exercise-associated hyponatremic encephalopathy, Clinical Journal of Sport Medicine, 18(4).]
“Older adults. As you age, your body’s fluid reserve becomes smaller, your ability to conserve water is reduced and your thirst sense becomes less acute.” [Mayo Clinic]
If you are urinating less then check for bloating as described under
Jack and his friends knew electrolytes are important during exercise. They’d been drinking plenty of sports drinks. Although they vary significantly these are the primary electrolytes in sweat. 1 liter contains approximately:
- 800 milligrams (mg) of sodium
- 115 mg of potassium
- Calcium and magnesium are present in small amounts
The exact amounts vary by individual depending on fitness, heat adaptation and other factors.
Compare the electrolytes in sweat with the concentrations in some popular sports drinks:
- Gatorade (1 liter)
- 460 milligrams (mg) of sodium,
- 130 mg of potassium
- No calcium or magnesium
- 60 grams (gm) of carbs (240 calories)
- Powerade (1 liter)
- 420 mg of sodium
- 100 mg of potassium
- No calcium or magnesium
- 60 gm of carbs (240 calories)
- HEED (1 liter with 2 scoops)
- 120 mg of sodium
- 62 mg of potassium
- 32 mg of magnesium
- 57 mg of calcium
- 54 gm of carbs (216 calories)
- Skratch (1 liter with 2 scoops)
- 800 mg sodium
- 80 mg potassium
- 100 mg calcium
- 80 mg of magnesium
- The Skratch website says “Drink when thirsty. Don’t when not.”
Note the sodium concentration in sports drinks except Skratch is roughly half the concentration of sodium in your blood, so you can drink too much of most sports drinks just as you can drink too much water.
Electrolyte supplements aren’t the answer, either unless you take enough tablets every hour:
- Nuun (1 tablet)
- 360 mg of sodium
- 100 mg of potassium
- Succeed! (1 capsule)
- 341 mg of sodium
- 21 mg of potassium
- Endurolytes Extreme (1 capsule)
- 120 mg of sodium
- 75 mg of potassium
According to the ACSM consuming additional sodium during events longer than four hours may reduce the risk of hyponatremia. The ACSM doesn’t recommend other electrolytes. [ACSM, 2007]
Heed Joe Friel’s recommendation: “Pay attention to your thirst mechanism. We’ve been taught over the past few years that it [thirst] is not effective and that we shouldn’t trust it. This ‘old wives’ tale’ refuses to go away. Drink when you are thirsty. When you’re not thirsty, don’t drink. It’s that simple.” [The Cyclist’s Training Bible (2009) page 257]
Next week: Coach Hughes Homemade Sports Drink [HMSD], which meets the recommendations of the ACSM at a fraction of the cost.
You can learn more about the science of riding in the heat, and managing your fluids and electrolytes, in my two-part eArticle series:
Cycling in the Heat, Part 1: Ride Management is 19 pages and covers
- Why you get hot while riding
- Effects of overheating
- Acclimating actively and passively
- How to train in hot months
- How to ride without overheating in all conditions
- How to stay (relatively) cool while riding
- What to wear in the heat
- What to eat and drink in the heat
- How to cool down if you overheat
- Heat-related problems
Cycling in the Heat, Part 2: Hydration Management is 21 pages and covers
- Assessing your sweat rate and composition
- How much should you drink?
- Fluid replacement
- Electrolyte replacement
- Electrolyte replacement drinks
- Electrolyte replacement supplements
- Electrolyte replacement food
- Hydration-related problems
The cost-saving bundled eArticles totaling 40 pages Cycling in the Heat Parts 1 and 2 are just $8.98 (a 10% savings)
Coach John Hughes earned coaching certifications from USA Cycling and the National Strength and Conditioning Association. John’s cycling career includes course records in the Boston-Montreal-Boston 1200-km randonnée and the Furnace Creek 508, a Race Across AMerica (RAAM) qualifier. He has ridden solo RAAM twice and is a 5-time finisher of the 1200-km Paris-Brest-Paris. He has written over 40 eBooks and eArticles on cycling training and nutrition, available in RBR’s eBookstore at Coach John Hughes. Click to read John’s full bio.