What would be my control variable?

I am doing a graph about blood pressure. The lab was to find the blood pressure of a person while they were resting. Then find the blood pressure after 5 minutes of exercise. Then find the blood pressure again 2 minutes after that. On the graph, time is on the bottom(independent variable) and blood pressure is on the y-axis(dependent variable). What is my control variable?|||Resting Blood pressure would be your control. Since it is an exercise lab, I am guessing you are expected to use the resting rate as your control.