What allows pulse rate to increase gradually?

The gradual increase in pulse rate is primarily regulated by the body's autonomic nervous system, particularly through the action of the sympathetic nervous system. During physical activity or stress, the body releases hormones like adrenaline, which stimulate the heart to beat faster and pump more blood to meet the increased demand for oxygen and nutrients. Additionally, factors such as improved cardiovascular fitness can enhance the heart's efficiency, allowing for a more gradual and controlled increase in pulse rate during exercise.