Exercise raises blood pressure because pressure is determined by the force of your heart contracting times the resistance of the blood vessels against the flow of blood. When you exercise, your heart muscles contract with much greater pressure to increase blood flow to your exercising muscles. However, studies have shown that lifting heavy weights does not cause sustained high blood pressure.
Normal blood pressure is under 120 when your heart contracts and under 80 when it relaxes. When you lift a heavy weight, such as when performing a leg press, your blood pressure can rise from 120 over 80 to 400 over 200. When you run, your blood pressure can rise to around 200 over 80. However, within minutes after you finish exercising, your blood pressure returns to normal. Regular exercisers have lower blood pressures than people who do not exercise. However, if you have a weak heart or high blood pressure, check with your doctor before starting a weight-lifting program.