While dehydration is a more common concern for exercisers, some experts think the public should be aware of the danger of drinking too much water, which can lead to a potentially fatal condition called hyponatremia.

Characterized by an abnormally low blood concentration of sodium, it is most often seen at extremely high-endurance events such as ultra-marathons.

Hyponatremia is more common among women than men, and was responsible for the death of a 43-year-old woman running in the Chicago Marathon last year.

Symptoms include nausea, vomiting, muscle weakness, headache and disorientation, and bloating in the face and hands.

Research suggests that drinking about two cups of fluid two hours before exercise and another six to eight ounces every 20 minutes can help optimize performance.

Some exercisers may opt to measure the amount of fluid they lose by weighing themselves before and after exercise to determine the number of pounds lost through perspiration. For every pound lost, experts recommend drinking one pint of fluid during exercise.

Sports drinks may also be a good choice because they help replace lost sodium and have been shown to enhance performance during prolonged exercise.