BENGALURU: Water is essential for life. From the time that primaeval species ventured from the oceans to live on land, a major key to survival has been the prevention of dehydration. The critical adaptations cross an array of species, including man. Without water, humans can survive only for days. Water comprises from 75 per cent body weight in infants to 55 per cent in the elderly and is essential for cellular homeostasis and life.
When we speak of water, we are essentially focusing first and foremost on all types of water – be it soft or hard, spring or well, carbonated or distilled water. Furthermore, we get water not only directly as a beverage but also from food and to a very small extent also from the oxidation of macronutrients (metabolic water). The proportion of water that comes from beverages and food varies with the proportion of fruits and vegetables in the diet.
Apart from urinary excretion, the other main fluid regulatory process is drinking, mediated through the sensation of thirst.The brain’s decision to start or stop drinking and to choose the appropriate drink is made before the ingested fluid can reach the intra- and extracellular compartments. The taste buds in the mouth send messages to the brain about the nature of, and especially the salt of the ingested fluid, and neuronal responses are triggered as if the incoming water had already reached the bloodstream.
Hydration status is critical to the body’s process of temperature control. Body water loss through sweat is an important cooling mechanism in hot climates and during physical activity. Sweat production is dependent upon environmental temperature and humidity, activity levels, and the type of clothing worn.
During challenging athletic events, it is not uncommon for athletes to lose 6-10 per cent of body weight in sweat loss, thus leading to dehydration if fluids are not replenished. Decrements in physical performance in athletes have also been observed under much lower levels of dehydration. Hypohydration appears to have a more significant impact on high-intensity and endurance activities such as tennis and long-distance running than on anaerobic activities such as weight lifting or on shorter-duration activities, such as rowing.
Strategies for hydration during exercise
During vigorous exercise (>70 per cent VO2max) understand that gastric emptying may limit fluid absorption. Athletes can train their gut to improve gastrointestinal comfort or adopt strategies to increase fluid intake before and after exercise.
Carefully monitor acute changes in body mass over an exercise bout to determine sweat rate, adequacy of fluid replacement and fluid needs for recovery for that session. Consider how well this can be used to evaluate general hydration strategies in similar situations.
Use changes in body mass, urine colour and thirst to track daily changes in hydration status.
Increase fluid replacement during exercise in hot and humid environments to account for increased sweat losses.
Modify fluid intake when exercising in cold or altitude according to an estimation of fluid losses noting that thirst may be less reliable as a guide to dehydration under these conditions.
Consider the risks of hyperhydration as well as hypohydration for any sporting event or individual athlete, and prepare appropriate practice and education strategies.
Consider body size, acclimatisation status and thirst drive when developing hydration plans for individual athletes.
During training, ensure that there is ample access to fluids that are palatable to athletes.
Understand the opportunities for fluid intake during that are specific
to a sport or event, and any other practical issues that determine fluid intake.