After a day of hiking, I get severe leg cramps in my calves. Can you explain why these are happening and what I can do to prevent them?
The exertion and fatigue of a long day on the trail can combine to cause lower leg cramps that have been compared to the bite of an alligator--without the teeth marks. The pain, in other words, can be excruciating. While dehydration aggravates the condition, salt depletion is the real culprit. Voluntary skeletal muscle bundles sometimes fire involuntarily and powerfully when salt is depleted, causing the intense pain you feel.
These cramps will ease rapidly, often within minutes, if you drink a salt solution when they start. You don't need much salt--no more than one-half teaspoon in a liter or quart of water. Feel free to increase palatability by adding a powdered fruit drink to the solution. If the drink is cool, temperature-wise, your stomach will empty it faster into the lower intestine, and it will get to work faster.
To prevent these cramps eat salty snacks on the trail and/or at mealtime, or add one-fourth to one-half teaspoon of salt to your water bottle when you refill. You might also consider consuming a sports drink, which often has enough salt to prevent the cramps.