Pay Attention to Your Thirst

Fluid replacement and exercise

Sport and athletic associations have stopped promoting the old mantra of "drink as much as possible." Instead, they have stressed the importance of proper fluid intake before, during, and after exercise.

How your body maintains fluid balance

The amount of water and salt in our bodies is balanced by an intricate system of hormones regulated by the kidneys and nervous system. During exercise, we increase our heart rate and the volume of blood pumped out of the heart with each beat. This is called cardiac output. With strenuous exercise, cardiac output can increase from 5-25 quarts per minute. Our bodies need a full tank of salt and water within our bloodstream to make this happen.

Meanwhile, as body temperature rises during exercise, we sweat to release the heat. Also, we breathe faster and harder, which causes more water loss. The body's response to the fluid loss is to tell our kidneys to hold on to all of the fluid they can. One of the key hormones that makes this happen is called ADH, or anti-diuretic hormone. ADH levels rise in response to fluid loss by telling the kidneys not to excrete water. So the amount of water relative to salt content in the blood rises, lowering the concentration of sodium.

How much water should you drink?

Attention to proper hydration starts before you exercise. Drink 16 ounces of fluid over 15-30 minutes, ending two hours prior to your planned exercise start time. If you have been eating normally with at least a little salt, then plain water is fine. If not, consider a sports drink or adding a pinch of salt and sugar to the water.

For moderate exercise lasting up to an hour, you can usually rely on thirst to drive your fluid intake. The exception is exercising outdoors in very hot or cold weather, when you should drink a little extra beyond thirst.

If you exercise regularly for longer than one hour at a time or plan to compete in a long-distance event, you should make a more accurate assessment of your personal fluid needs. A simple estimate can be made by measuring change in body weight. Empty your bladder and get on the scale in dry clothing. Exercise for one hour at your usual or expected pace. Measure the exact amount of water that you drink during the test hour. Empty your bladder again and dry off any excess sweat. Put on the same dry clothes you wore for the initial weight and get back on the scale.

The amount of fluid you need per hour of exercise equals the number of ounces you drank plus the difference in ending vs. starting weight. (One pound equals 16 ounces of fluid.)

After you finish competing or working out, pay attention to thirst and keep drinking until urine color returns to normal — usually a pale yellow.

Regarding the type of fluid to drink, sports drinks or homemade solutions with a little sugar and salt are not necessary unless you plan to exercise for more than a couple of hours. Some people, however, feel more energized using these drinks with even less strenuous workouts.

Race course water stations

There will be plenty of water stations along the Blue Cross Broad Street Run course. Gatorade will also be provided at the 2.2-, 6.1-, 7.8-, and 8.5-mile water stations and at the finish. The Gatorade will be in bright green cups on the left side of the last tables of each station. Bottled water will be available at the finish line.

The water stations are located at the following mile marks:


  • 2.2 miles
  • 4.2 miles
  • 4.9 miles
  • 5.2 miles
  • 6.1 miles
  • 6.8 miles
  • 7.8 miles
  • 8.5 miles
  • 9.1 miles
  • Finish
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