Dehydration – lack of fluids increasing the chance of heat injury.

Hyponatremia – too much water intake leading to dilution of salt in the body

Risk Factors For Hyponatremia
Sustained activity greater than 4 hours
Excessive water intake 1 to 2 days before event
Taking medications such as ibuprofen or naproxen
Certain prescription medications
Female gender

Symptoms of Both
Swelling and tightness of the hands and feet
Fatigue, weakness
Light-headedness and dizziness
Cramps and muscle spasms
Nausea, vomiting
Muscle aches
Bizarre behavior, combativeness, hallucinations

Determine your “sweat genetics” – weigh yourself before and after an hour of intense exercise. For every pound lost, replace with 16 ounces of fluid per hour of your event. You may need to adjust this with weather conditions.

Pay attention to thirst – if you are thirsty, you probably need to drink.

If exercising more than an hour, be sure to replace your sodium by increasing the salt in your diet a couple of days before your event and by using sports drinks that contain sodium.

Avoid salt tablets due to excessive sodium content.

Avoid nonsteroidal anti-inflammatory medications such as naproxen or ibuprofen before or during your race.

If you are on prescription medications, ask your doctor if any of your medications have an effect on the concentration of sodium in your body.

If during or after the race you begin to have any of the symptoms described, be sure to stop and seek medical attention.