Water and electrolytes serve very important roles in the maintaining proper functioning within the body, and sweating can lead to excessive loss of both critical nutrients and electrolytes if not properly replaced. Dehydration adversely impacts health and exercise performance. To avoid excessive fluid and electrolyte losses, a person should begin exercising in a well-hydrated state. This means prior to strenuous exercise, drink approximatively 20 fl oz (500 ml) of liquid to ensure proper hydration at the onset of exercise.
Even minimal dehydration (one percent body weight) can increase cardiovascular strain and limit the ability of the body to transfer heat from contracting muscles to the skin surface for dissipation to the environment. Remember, deficient body fluids will increase the probability of compromising your exercise performance and developing heat-related injuries.
Summary of dehydration symptoms:
- Thirst: dry mouth
- Slower reaction time: reduced concentration
- Impaired judgment: confused, loss of balance, dizzy
- Reduction in blood volume: defined as less cardiac output available to the working muscles. Causes fatigue in your muscle resulting in less performance capabilities.
- Decreased skin blood flow: your skin won’t cool down as fast from physical exertion.
- Decreased sweat rate: you aren’t sweating as much
- Decreased heat dissipation: you can’t cool down as fast as usual.
- Increased core temperature: your body can’t cool down
- Increased rate of muscle glycogen use: your body has less ability to ingest carbohydrates which will increase fatigue.
Summary of injuries resulting from severe dehydration
- Muscle cramps
- Delayed muscle pain attacks
Consuming sufficient fluids during exercise will influence cardiovascular, thermoregulatory and muscle function, as well as hydration status. To avoid dehydration, 13-32 fl oz (400-1,000 ml) of fluids should be consumed every hour by drinking small amounts frequently: 3-8oz (100-250ml) every 15 minutes. Water is fine if the exercise is of short duration, however, if the exercise is longer that one hour, the fluid should contain carbohydrates (from sugars) and electrolytes (from salts). The addition of carbohydrates to a fluid replacement drink can enhance intestinal absorption of water and help maintain blood glucose concentration during exercise, which may preserve muscle glycogen (sugar storage) and thereby delay fatigue.
Sustained exercise, especially in the heat, can result in high sweat rates and substantial water and electrolyte loss. If sweat water and electrolyte losses are not replaced, performance and overall health can be severely compromised. Dehydration and electrolyte deficits have been associated with muscle cramps. Conversely, excessive fluid intake can result in hyponatremia (low salt levels in the blood) which can be life threatening. Fluid intake should be limited to one quart (one litre) per hour to avoid hyponatremia. Women may be at greater risk than men of developing exercise-associated hyponatremia.
Exercise increases physical stress to the body and people partaking in physical recreation need to pay special attention to their fluid, carbohydrate, and salt intake. Thirst is your best indicator of dehydration: if you are thirsty when exercising, you are dehydrated.