Which of the following symptoms indicates heat cramps?

Heat cramps are painful involuntary muscle contractions that usually occur during strenuous physical activity in high temperatures. The characteristic symptom that distinguishes heat cramps is the occurrence of large muscle spasms, particularly in the legs and abdomen. These cramps happen when the body loses a significant amount of water and electrolytes through sweat, leading to muscle fatigue and strain.

While other symptoms like nausea, increased heart rate, or fatigue can occur due to heat-related illnesses, they are not specific indicators of heat cramps. Nausea and fatigue could indicate heat exhaustion or other heat-related disorders, while an increased heart rate can occur as the body works harder to cool itself and maintain blood flow to the skin. In contrast, large muscle spasms are the definitive symptom that indicates heat cramps, making it the correct choice for this question.