If you exercise or do physical work in the heat long enough, you can lose fluid and salt in your sweat. This can cause sharp pains, especially in your arms, belly, and calves. To keep this from happening, you need to take in fluids and salt. You can drink a sports drink or eat a salty food with water. In a pinch, you can make your own sports drink by mixing a teaspoon of salt in a quart of water.