If you experience fatigue and blurred vision during or after exercise, you may be dehydrated, have low blood sugar or not be rested enough. If the problem happens consistently, you may have an underlying medical disorder such as low blood pressure or a heart problem. Consult your doctor if adjusting your diet, hydration and sleep habits does not resolve the problem.
Hypoglycemia
When you are not properly nourished, your glucose level -- also referred to as blood sugar -- can get too low. Glucose is the body's main source of fuel. If you do not have enough of it, your body cannot function properly and the problems can be made worse by exercise. Symptoms of hypoglycemia can include blurred vision, fatigue, headache, dizziness, excessive sweating, trembling and confusion. Hypoglycemia is common in diabetics who take medication for insulin, but can happen if you go too long without eating or exercise too strenuously.
Dehydration
Dehydration results when you lose more fluid than you take in, which can happen if you are sweating a lot during exercise or not consuming enough fluids before exercise. If you are dehydrated, your body does not have enough water and other fluids to carry out its normal functions, which include regulating blood pressure. Water fills out the blood plasma, and if it's lacking, your blood pressure can drop, leading to fatigue and blurred vision. Other symptoms of mild dehydration can include dizziness, headache, thirst and a dry, sticky mouth.
Other Causes
Dehydration and hypoglycemia are common causes of blurred vision when exercising, but there are many others -- some more serious than others. Lack of proper sleep can lead to poor concentration, blurred vision and fatigue. Low blood pressure, or hypotension, can lead to not enough blood flowing through your body and to your brain, which can lead to, among other symptoms, fatigue and blurred vision. Not having enough iron in your blood, medically referred to as anemia, can cause similar symptoms. In more serious cases, an underlying heart problem needing medical attention could be the cause.
Response
If you experience fatigue and blurred vision while exercising, stop and rest. Consume a small snack high in carbohydrates or sugar, such as peanut butter and crackers or a glass of orange juice. Drink some water if you feel thirsty or have been sweating a lot. Drinking water or a sports drink enhanced with electrolytes can help your body hydrate more quickly. If you start to feel faint or the blurred vision and fatigue do not dissipate, refrain from further exercise and seek medical attention.
Prevention
To avoid dehydration, start hydrating the day before you exercise. Drink one to three cups of water right before exercise, and drink plenty of water during and after exercise, particularly if you sweat a lot. To avoid hypoglycemia, eat a small-to-medium-size meal at least two to four hours before you exercise. Include plenty of complex carbohydrates such as rice, pasta and other grains. If you missed a meal, eat a small snack at least 30 minutes before you exercise. Get plenty of sleep the night before exercise. If you make changes in your eating, drinking and rest habits, and you still experience fatigue and blurred vision while exercising, consult a doctor.
