What does vigorous-intensity physical activity primarily cause?

Vigorous-intensity physical activity is characterized by a significant effort that leads to a substantial increase in heart rate. This level of intensity engages the cardiovascular system effectively, causing the heart to pump more blood to meet the heightened demands of the muscles being used. During such activities, individuals often find that they can only speak a few words without pausing to catch their breath, further indicating the increased heart rate and overall exertion compared to moderate-intensity activities.

The physiological response to vigorous-intensity activity includes increased oxygen consumption and elevated heart rate, both of which are pivotal for improving cardiovascular fitness and overall stamina. This is why the answer highlighting the substantial increase in heart rate aligns well with the recognized characteristics of vigorous exercise.