Which of the following is an effect of aerobic exercise on the cardiovascular system?

Engaging in aerobic exercise brings about significant changes in the cardiovascular system, one of which is a lower resting heart rate. This effect occurs because regular aerobic training enhances the efficiency of the heart. As the heart becomes stronger and more efficient, it requires fewer beats per minute to pump the same volume of blood, leading to a lower resting heart rate.

This physiological adaptation means that the heart can effectively supply oxygen-rich blood to the muscles and organs with less effort. A lower resting heart rate is also indicative of improved cardiovascular fitness, suggesting that the heart can handle physical activity more efficiently and recover more quickly after exertion.

Other options do not directly pertain to the effects of aerobic exercise on cardiovascular health. Increased muscle mass relates more to resistance training, increased bone density is primarily seen through weight-bearing exercises, and decreased blood circulation contradicts the benefits one would expect from aerobic activity, which typically improves circulation throughout the body.