Final answer:
Among VO2 max, blood pressure, high-density lipoproteins (HDL), and heart rate, HDL is the least sensitive to exercise because it changes more gradually with regular physical activity, providing long-term cardiovascular benefits.
Step-by-step explanation:
The variable least sensitive to exercise (training) among the ones listed is high-density lipoproteins (HDL). VO2 max, heart rate, and blood pressure are all promptly affected by exercise. VO2 max indicates the maximum amount of oxygen the body can use during intense exercise, and it typically improves with endurance training. Heart rate increases dramatically during exercise to meet the body's increased demand for oxygen and nutrients. Blood pressure rises during exercise as a result of the increased cardiac output and elevated heart rate. However, HDL levels change more gradually in response to regular exercise and offer long-term cardiovascular benefits such as reducing the rate of plaque formation and lowering the overall cholesterol levels in the body.