A lot of people were having muscle cramps on Skyline yesterday. Although it wasn't hot, it was warm for those of us who live in more temperate climates (Riverside, Orange County, San Diego) and who normally start hiking at 5 to 6 K.
Warm, dry weather can cause significant sweat losses and people may not be aware of how much fluid they're losing. In addition to water losses, sweating results in losses of electrolytes, especially sodium and chloride (salt). Muscle cramps are caused by sodium losses, not potassium or magnesium.
Although the amount of salt in sweat varies, most people lose about 800 mg for every two pounds (one quart) of sweat. Some people are salty sweaters and lose much more, regardless of their fitness level or degree of heat acclimation. Salty sweaters generally have white stains on their shirts/shorts and the sweat burns the eyes.
Heat-related muscle cramps occur during prolonged exercise when there has been profuse and prolonged sweating. Muscle cramps can occur when the salt lost in sweat isn't replaced. Hikers/athletes who are prone to heat cramps have high sweat rates and/or lose a considerable amount of salt in their sweat.
Prevention is always best. Eating salty foods and/or consuming a sports drink with salt can replace sodium losses and maintain hydration (the body needs salt to retain water).
For cramp prone people, it may be helpful to add additional salt to the sports drink -- 1/4 to 1/2 teaspoon of salt to 32 ounces of sports drinks. Some sports drinks contain a higher amount of salt -- Gatorade Endurance and Powerbar Endurance. Both provide about 800 mg per quart.
If you're drinking plain water while hiking in warm weather, it's even more critical to have a source of salt. Sources of salt:
1) Table salt -- 1/2 teaspoon has 1000 mg of sodium -- close to the amount hikers lose in 2 lbs of sweat. You can carry salt in a baggie, carry those little fast-food salt packets, or even salt your water (which isn't appealing to most people).
2) Salt tablets -- vary in sodium from 100 to 1000 mg per tablet. I am not a fan of Endurolytes as they don't provide enough sodium. Cramps are caused by sodium losses. I recommend using a salt tablet that provides at least 500 mg.
3) For those folks who can't do sports drinks, NUUN can be added to plain water. It's flavored so you don't notice the salt.
4) Salty foods. Pretzels, beef jerky, baked or regular chips, salted nuts, salted crackers.
5) Carbohydrate gels with a higher sodium content = 200 mg per gel.
How much sodium? Depends on your sweat rate and how much sodium you lose. I am a salty sweater. I drank three quarts of Gatorade Endurance yesterday (2400 mg) and ate three PowerGels with 200 mg of sodium (600 mg). Total = 3000 mg. It took me 5.5 hours, so I consumed about 500 mg per hour.
Prior to my jacked up spine, I did marathons and the Ironman triathlon. I work with endurance athletes to improve their performance and help them feel better when they compete. Skyline is an endurance activity, as is hiking Whitney or the Grand Canyon. My goal with hiking nutrition is to help people feel better when they hike.
Miles of smiles,