Water is a nutrient “sui generis” because, although it does not provide calories, it is a source of micronutrients and is indispensable for life. It is particularly important for a sportsman or an athlete, as body hydration directly affects sports performance. Sweating is the main way to disperse the increase in body temperature induced by exercise; therefore sweating leads to dehydration of body fluids and a reduction in thermodispersive capacity.
Already a reduction in body weight due to dehydration of 2 percent results in a deterioration in sports performance. Higher levels of dehydration correspond to increasingly marked physiological alterations (decrease in muscle work capacity, onset of muscle cramps, gastrointestinal disorders, alteration of temperature control). For self-control hydration use google apps: https://play.google.com/store/apps/details?id=reminder.drink.water
A dehydration equal to 2.5 per cent of body weight corresponds to an increase in the perception of effort (RPE) according to the Borg scale and a decrease in specific skills of the footballer (sprint, dribbling, decision making index).
Particular attention should also be paid to the hydration of children in developmental age who attend football schools: children have less efficient thermoregulation than adults and are more prone to water loss than adults because they have a higher ratio of body surface to body mass. Moreover, various evidences in the literature suggest that children already before the afternoon sports activity go to school in a state of hydration deficit. There is little evidence, however, for female football, but the available evidence suggests that female football players also suffer from dehydration while showing a lower rate of sweating and loss of electrolytes than men.
Recommended hydration strategies
In the pre-race
Four hours before the match moisturize with 5-7 ml/Kg (for a footballer of 70 kg is equivalent to a volume between 350 and 500 ml of fluid) and monitor the color of urine and frequency of urination; if the color of urine is still intense, two hours before the match drink another 3-5 ml/Kg.
During the competition
The purpose of hydration during the competition is to prevent excessive dehydration (>2 per cent of body weight) and the loss of salts that can compromise sports performance; take advantage of breaks, changes and the interval to drink in small sips; essentially hydrate with water (fresh, but not cold); in some conditions it is possible to use sports drinks with 6-8 per cent carbohydrates (based on maltodextrin and/or fructose) thus also obtaining a glycidic supplement in order to save the loss of muscle glycogen.
After the race
The priority is to reintegrate the lost water and mineral salts; the volume to reintegrate (in litres) is calculated by subtracting from the weight in Kg before the training/race the weight after the training/race and multiplying this difference by 1.5; use mineral water with a good mineral content; sport drinks or some drinks with a high rehydrating power even higher than the water itself, such as milk, can be useful, depending on the environmental conditions. In order to evaluate the state of hydration of a footballer, it is sufficient to carry out a bioimpedance analysis, which allows to determine both the total quantity of water and its compartmentalization.
It is not always possible to carry out such an analysis and in this case “field” measurements such as the determination of the specific weight of morning urine or urinary osmolality can be used. From various evidence in the literature there are cutoffs that allow to correlate the results with the state of hydration of the football player (for the specific weight the limit of 1020 according to the ACSM stand position is valid).
The athlete will be instructed to self-assess his state of hydration, comparing the intensity of the urine color with a reference color urine chart (from 1 to 3 for normal hydration, from 4 to 5 for mild dehydration, from 6 to 8 for severe dehydration).