Fluid and Electrolyte Requirements

Fluid needs vary greatly from person to person, so it's hard to make a one-size-fits-all recommendation. Sweat rates commonly range between 1 and 4 pounds (0.5 to 2 quarts, or 480 ml to 2 L) per hour, depending on your sport, body size, intensity of exercise, and clothing; the weather conditions (hot or cold); whether or not you are heat acclimatized; and how well trained you are. Sweat rates for a 110-pound (50 kg) slow runner might be 1 pound (16 oz, or 480 ml) of sweat per hour, while a 200-pound (91 kg) fast runner might lose about 4 pounds (2 qt, or 2 L) per hour. Even fast swimmers sweat—almost a pound per hour of training. Football players wearing full equipment in the summer heat might lose more than 16 pounds (2 gal, or 8 L) of sweat in a day.

On a daily basis, the simplest way to tell if you are adequately replacing sweat loss is to check the color and quantity of your urine. If your urine is very dark and scanty, it is concentrated with metabolic wastes, and you need to drink more fluids or eat more foods with a high water content such as cooked oatmeal, yogurt, and fruit. (Most people get 20 to 30 percent of their fluids from foods; some people actually eat all their daily water requirement.) When your urine is pale yellow, your body has returned to its normal water balance. Your urine may be dark if you are taking vitamin supplements; in that case, volume is a better indicator than color. For specific colors, search the Web for "urine color chart."

In addition to monitoring urine and weight loss, you should also pay attention to how you feel. If you feel chronically fatigued, headachy, or lethargic, you may be chronically dehydrated. This is most likely to happen during long hot spells in the summertime. Dehydration can be cumulative.

Water..

  • in blood transports glucose, oxygen, and fats to working muscles and carries away metabolic by-products such as carbon dioxide and lactic acid.
  • in urine eliminates metabolic waste products. The darker the urine, the more concentrated the wastes.
  • in sweat dissipates heat through the skin. During exercise water absorbs heat from your muscles, dissipates it through sweat, and regulates body temperature.
  • in saliva and gastric secretions helps digest food.
  • throughout the body lubricates joints and cushions organs and tissues.

150 lb man

Sweat contains more than just water; it has electrically charged particles that help keep water in the right balance inside and outside of cells. The amount of electrolytes you lose via your sweat depends on how much you sweat, your genetics, your diet, and how well you are acclimatized. The following chart shows the electrolyte loss that can occur with sweating.

Electrolyte

Average amount/2 lb (1 L, ~1 qt) sweat

Food comparison

Sodium

800 mg (range 200-1,600)

1 qt Gatorade = 440 mg sodium

Potassium

200 mg (range 120-600)

1 med banana = 450 mg potassium

Calcium

20 mg (range 6-40)

8 oz (230 g) yogurt = 300 mg calcium

Magnesium

10 mg (range 2-18)

2 tbsp peanut butter = 50 mg magnesium

Muscle cramps are believed to be associated with dehydration, electrolyte deficits, and muscle fatigue. If you sweat profusely, are left caked with salt, and experience cramps, take extra care to drink plenty of sodium-containing fluids while exercising. If your diet has a high salt content, you can likely replace sodium losses after exercise with standard postexercise meals. But consuming extra salt on your food if you had high sweat losses can be a smart way to enhance recovery, retain fluid, and stimulate thirst.

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