When normal conditions exist in the body, various mechanisms preserve fluid and electrolyte balance. If the mechanisms fail due to illness, stress, exercise, climate variations, supplements, foods, or beverages, life threatening imbalances may occur.
Body water in humans varies with age and sex. About 45% to 50% of body weight in females is water. Since males generally have higher amounts of lean mass, body water is around 50% to 60%.
Body water can be found inside of cells, which makes up about 2/3 of total body water, and surrounding cells, which makes up about 1/3 of total body water.
The electrolyte content of these fluids differs greatly. Outside of cells, sodium, chloride, and bicarbonate are the primary electrolytes. Within cells, potassium, magnesium, and phosphate are the primary electrolytes, which is why researchers can use radiolabeled potassium as a marker of lean tissue change.
If the output of fluids exceeds the intake of fluids, an imbalance occurs, and dehydration can develop. The severity of dehydration can be measured by weight loss as a percentage of the normal body weight.
Symptoms of dehydration include:
- Dry skin
- Fatigue and weakness
- Increased Body Temperature
- Muscle Cramping
- Darker-coloured urine
- Dry mucous membranes (mouth, nose, eyes)
Severe dehydration can also include:
- Muscle Spasms
- Dark urine
- Vision problems
- Loss of consciousness
- Kidney and liver failure
Why Is Dehydration So Important?
Water provides the medium for the solubility and passage of nutrients from the blood to the cells and the return of metabolic by-products to the blood.
Countless metabolic reactions in the human body rely on water as a medium.
Sensible body water loss (i.e. water loss that we know is occurring) occurs daily in the stool (200 ml), urine (500 to 1500 ml) and sweat. Insensible losses (i.e. those we cant perceive) occur through the skin (500 ml) and respiratory tract (400 ml). These vary with humidity, environmental temperature and respiratory rate.
When body water levels change, it can have significant effects throughout the body, including athletic performance. Indeed, dehydration of as little as 1% body weight (2 lb for a 200 lb person) is enough to reduce both endurance and strength performance as well as cognitive performance.
Be aware of thirst cues.
If no fluids are going to be given during exercise, you can pre-hydrate with the following regimen:
- 500 ml of fluid on the night before exercise
- 500 ml in the morning
- 500 to 1000 ml, 1 hour before exercise
- 250 to 500ml, 20 minutes before exercise
Consume nutrient dense foods/beverages after exercise to assist in the re-hydrating process.
Those with a history of cramping and salty sweat should consider adding salt to foods/beverages after exercising (a quarter to one-half teaspoon).
For every pound of sweat lost during exercise, rehydrate with 2 cups of fluid.
Dark colored urine can be indicative of a low water reserve in the body. So make sure your urine is light-colored and clear.