Diastolic blood pressure is the pressure on your artery walls between heartbeats. Diastolic pressure usually is described in combination with systolic pressure (the pressure exerted on your arterial wall during the heart’s contraction), and is the lower of the two numbers in your blood pressure reading. In healthy individuals, diastolic blood pressure stays the same during cardiovascular exercise.
Exercise and Diastolic Blood Pressure
There are several factors that affect diastolic blood pressure, including the amount of blood in your body (blood volume), the volume that your blood pumps into your arteries with each beat (stroke volume) and how often your heart is pumping new blood into the arteries (heart rate). To meet your muscles’ increased oxygen demand, all these factors increase during exercise. To create more space for the increased blood flow during exercise, your arteries dilate so diastolic blood pressure remains the same.
Your diastolic blood pressure is not exactly the same all day long. Your artery walls expand and contract to create the pressure that will help deliver blood most efficiently to different body parts, no matter your activity level. When you’re upright (either walking or standing in place), the arterial pressure must help the blood overcome gravity to reach the body parts above your heart. When you’re lying down (swimming or reading a book), blood doesn't have to overcome gravity, so your artery walls relax and your diastolic blood pressure stays low.
Exercising with Hypertension
Not everyone’s diastolic blood pressure stays the same during exercise. If you have blocked or stiff arteries, they may not be able to expand enough to allow for increased blood flow during exercise, therefore increasing diastolic pressure. Blocked and inelastic arteries can be caused by poor diet, age, genetics or lifestyle factors. Exercising diastolic pressure increasing more than 20 mmHg above resting values (or greater than 115 mmHg) is a sign that your body can’t cope with the demands placed on your cardiovascular system, and you should stop exercising immediately.
Low Blood Pressure and Exercise
Diastolic blood pressure can drop dangerously low immediately following exercise. If your heart rate drops before the arteries have a chance to contract, your heart won't pump enough blood to fill the widened arteries. Without enough blood, diastolic pressure drops and oxygen can't reach the brain. A cool-down period at the end of your workout brings your heart rate down slowly and allows your arteries time to contract, maintaining diastolic pressure. Athletes who already have low blood pressure should drink fluids during their workouts to prevent a further drop in blood volume (and therefore pressure) from dehydration.
Check with your doctor to make sure you are healthy enough for exercise. Patients with severe hypertension (a systolic pressure greater than 175 mmHg) should not exercise. Individuals with hypertension should not do any strenuous or heavy lifting and never should hold their breath while lifting weights.