Which physiological change should NOT occur during a warm-up?

During a warm-up, the goal is to prepare the body for physical activity by gradually increasing the heart rate, breathing rate, and muscle temperature. A lower heart rate would not be a physiological change associated with warming up, as the heart rate needs to increase to improve blood flow to the muscles and enhance oxygen delivery. A warm-up is designed to elevate the heart rate into the target exercise zone, making option A, which indicates a lower heart rate, the correct choice for what should not occur.

In contrast, an increase in breathing is expected as the body requires more oxygen to fuel the muscles during exercise. Likewise, an increase in body temperature is beneficial as it helps improve muscle elasticity and overall performance. Lactic acid build-up is typically associated with higher intensity exercise when the body relies more on anaerobic metabolism. During a warm-up, the metabolic demands are not yet elevated to that level, making it unlikely for lactic acid to accumulate significantly at that stage.