Syncope is the medical term for fainting. Following a bout of exercise, any dizziness or blurred vision is often directly related to environmental or external stress put on the body. In many instances it is an isolated incident. Repeated bouts of post-exercise dizziness or syncope often warrant a physical exam Triggers that can initiate feeling lightheaded and losing consciousness include environmental temperature, dehydration, low blood pressure and low blood sugar.
Hot and Cold Emergencies
Heat illness is often experienced by individuals during the summer months due to increased humidity and temperature. Athletes or individuals training through extreme temperatures must monitor heart rate, breathing and body temperature to avoid overexertion. Signs of post-exercise heat illness include the inability to sweat, muscle-cramping, nausea, dizziness, blurred vision, syncope, and in extreme circumstances coma or death. Hypothermia and other cold emergencies can also cause syncope. When an individual cannot keep his body temperature up, he may go into shock and lose consciousness. A 1999 study published in the American Family Physician stated that hypothermia and heatstroke were present in 15 percent of endurance runners who experienced exercise-related syncope.
Dehydration
Dehydration occurs when the body does not have enough water or electrolytes to perform normal physiological activity and cellular functions. Dehydration may occur in warm temperatures, after high intensity- or long-duration exercise. Signs of post-exercise dehydration include dizziness, fainting, nausea, vomiting. Older adults, individuals taking diuretics or individuals exercising while ill may be at increased risk for dehydration.
Blood Pressure
Fainting can occur when there is a sudden drop in blood pressure. Changes in blood pressure cause a decrease in blood flow. When blood supply is compromised, even for a few seconds, the brain is deprived of oxygen. Fainting may be more prevalent with weight-training and during the starting and stopping phase of cardio-exercise. Individuals often incorrectly hold their breath, which decreases their oxygen supply or they may change direction of motion too quickly. A momentary decrease in oxygen can cause dizziness, blurred vision and syncope.
Blood Sugar
Our brain and our muscles rely on a regular supply of blood glucose to function. Glucose, or sugar, is the primary energy source of cells. Low blood sugar is often associated with diabetes but can affect anyone who has not eaten sufficient calories prior to and during exercise. Low blood sugar is know as hypoglycemia. Individuals attempting to exercise on an empty stomach, while dieting, or at a higher intensity than normal may feel lightheaded, dizzy and eventually pass out. Hypoglycemia can be prevented by eating a pre-exercise snack. Portable pre-workout snacks include yogurt, fruit or granola bars.
References
- NINDS; "Syncope Information"; October 2010
- Mayo Clinic; "Vasovagal Syncope"; 2010
- American Family Physician; "Exercise-Related Syncope in the Young Athlete: Reassurance, Restriction or Referral?"; Francis O'Connor, et al.; November 1999
- PubMed Health' "Dehydration"; August 2009
- The Merck Manual; "Heart and Blood Vessel Disorders"; 2007
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