Painful, brief muscle cramps. Heat cramps generally occur after exercise or work in a hot environment or begin a few hours later. The most common muscles involved are the thighs, shoulders and calves. Patients who are not used to working in hot weather and those who sweat a lot are at increased risk for this disorder. Drinking fluids without any salt intake may also increase the chance of getting heat cramps. Heat cramps generally resolve on their own without specific treatment.