If you feel dizzy or lightheaded, you may have low blood pressure. During exercise, your body pumps more blood than usual. When you stop exercising abruptly, your heart beats more slowly but your blood vessels remain dilated, leading to lower blood pressure. Dizziness and lightheadedness may also indicate a heart problem. If you feel dizzy and experience low blood pressure during exercise, stop immediately and consult a physician.
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Low Blood Pressure
Symptoms of low blood pressure, or hypotension, include dizziness and fainting. Measure your blood pressure before running and check it again during exercise to monitor changes. Blood pressure measurements include a systolic reading, which indicates the force of your heart beating, and a diastolic reading which indicates blood pressure while your heart is at rest. Systolic blood pressure increases slightly during exercise, while diastolic remains the same or lowers slightly. If your systolic blood pressure fails to rise, or rises more than 10 mmHg, you may have a heart problem.
Heartbeat irregularities, such as bradycardia, heart-valve problems, heart attack and heart failure cause low blood pressure because they limit the amount of blood your heart can pump. Bradycardia means having an extremely slow heart rate, and it results from interference to electrical signals that stimulate heartbeats. The most common heart valve problem is mitral valve prolapse, which affects 2.5 to 5 percent of the population. Mitral valve prolapse is an inherited disorder that causes back-flow of blood in the heart chambers.
Dehydration and Nutrient Imbalance
Other causes of low blood pressure and dizziness include dehydration and nutrient imbalances. Sweating is your body's natural mechanism for cooling off, especially during exercise, which increases body heat. When you sweat, you lose water and electrolytes such as sodium, potassium, calcium, magnesium, chloride, bicarbonate, phosphate and sulfate. Failure to resupply your body with fluids and nutrients leads to dehydration, dizziness and lower blood pressure.
Try cooling down from workouts more gradually if you experience low blood pressure toward the end of exercise. Slow from a run to a jog and then a brisk walk over 10 minutes, for example. Drink fluids throughout the day to prevent dehydration, and drink small amounts of water or sports drink during exercise. Use sports drinks with 6 to 8 percent carbohydrate to rehydrate and replenish electrolytes, especially if you exercise intensely or for prolonged periods. Try taking vitamin B12 and folate supplements to prevent anemia-related low-blood pressure.