If you experience headaches or dizziness when exercising, you may be experiencing hypoglycemia, or low blood sugar levels. Your body converts food into glucose, a type of sugar, and uses it for immediate energy needs or stores it in your muscle and liver cells as glycogen to use between meals or during exercise. Exercise, especially strenuous exercise, can deplete glycogen stores and cause you to experience symptoms of hypoglycemia.
Carbohydrates as Fuel
When you begin your workout, your body takes glucose in your bloodstream or glycogen in your liver and uses it to propel your muscles. After 15 minutes, you rely on liver glycogen stores. When those are depleted, you turn to fat as an energy source. An unfit person consuming 45 percent of her calories from carbohydrates, stores 100 grams of glycogen in her liver. At a moderate exercise pace, you burn 1 gram of glucose per minute and would theoretically completely diminish your glycogen stores after 1 hour and 45 minutes of exercise.
When glycogen stores are depleted, you also experience hypoglycemia. According to the University of Maryland Medical Center, your brain relies on glucose for fuel, so without sufficient amounts, you can experience dizziness, sweating, blurred vision, headache, loss of coordination, anxiety, irritability and heart palpitations. If you don't get more sugar into your system, it can lead to seizures, coma, permanent brain damage and even death.
Low Blood Sugar Prevention
Eat complex carbohydrates before working out if you are prone to symptoms of low blood sugar. Complex carbohydrates include whole-grain breads, cereals and pastas and vegetables. While exercising for long periods, eat or drink simple carbohydrates, such as sports drinks and pretzels. The University of Maryland Medical Center states that exercise-induced hypoglycemia several hours after a meal doesn't typically cause serious symptoms. Blood sugar levels can be quickly elevated again with a slice of bread or glass of orange juice.
Exercise does decrease your blood sugar levels, but regular hypoglycemic episodes after exercise are not common in otherwise healthy people, according to NetDoctor. Speak with your doctor if you frequently experience these episodes. If you are not diabetic, the causes of hypoglycema include too much insulin in your blood, problems with your adrenal or pituitary glands, malnutrition or liver problems.
- Centers for Disease Control and Prevention: Carbohydrates
- University of Maryland Medical Center: Hypoglycemia
- Joslin Diabetes Center: Why Is My Blood Glucose Sometimes Low After Physical Activity?
- Marathon Training: The Science of Carbohydrate Loading
- NetDoctor: Hypoglycemia (Low Blood Sugar) in Non-Diabetic People