Hydration and Dehydration
Dehydration occurs when fluid losses exceed 1% of body weight. Symptoms include headache, irritability and fatigue. Fluid replacement is needed before, during and after physical activity. This is critical in preventing dehydration. Water is important in physical activity and is the one nutrient most often neglected by people. Water is essential for temperature control, circulation, and urine production. Proper fluid replacement before, during and after physical activity actually influences you're performance. Water's most important function in physical activity is its role in acting as a coolant for working muscles and maintaining normal body temperature. During exercise, heat is lost primarily through evaporation.
When sweat evaporates, heat is released from the blood circulating near the skin, cooling the body. Sweat losses of 1 to 2 litters per hour are not excessive during exercise in the heat. The body also sweats in cold whether making adequate hydration an important consideration during physical activity in cold environments. Sweat loss also occurs during participation of water sports. Dehydration compromise heat dissipation causing the body's temperature to rise and loss of coordination. Fluid losses cause a decrease in oxygen consumption which results in a reduction of work capacity. Thirst is not the best indicator of the body's water needs. Fluid should be consumed at regular intervals during physical activity.
What about Electrolyte Loss?
Although electrolytes are lost in sweat, the loss of water is considerably larger. During endurance events (marathons, triathlons, ultra-marathons) in warm climate electrolyte loss can be critical. The environmental condition, fitness and severity of sweat losses must be consider. Although the total amount of electrolytes and minerals in the body is relatively small, each is vital for cell function. They have regulatory roles as well as providing structure for formation of bones and teeth. Electrolytes and minerals, like vitamins, can be usually obtained in the required amounts in a balanced diet. The Electrolytes of concern include sodium and potassium which are located primarily in body fluids. They are the main electrolytes lost in sweat. The major minerals of interest are: Calcium, the major component of bone and teeth; Iron, an essential component of hemoglobin (Hgb) which carries oxygen through the body.
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